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Full text of "Practical Electronics 1970 October"

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ADCOL A Soldering 
Instruments add to 
your efficiency 



ADCOLA 64 

for Factory Bench 
Line Assembly 

A precision instrument — supplied 

with standard 3/1 6" (4.75 mm) 

diameter, detachable copper 

chisel-face bit*. 

Standard temp. 360°c at 23 

watts. 

Special temps, from 250°c — 

410°c. 

'Additional Stock Bits 

(illustrated) available 
COPPER 




EYELET BIT 



B 58 'A " — 6-*+ mm CHISEL FACE 

LONG LIFE 

B 42 LL -h" 4.76 mm CHISEL FACE 



B38LL §' — **i 



B14LL A' — *■* 

'-- - 



Ri 



B44 LL ft- — 



CHISEL FACE 



CHISEL FACE 



SCREWDRIVER 




Don't take chances. We don't. 
All our ADCOLA Soldering 
Instruments are of impeccable 
quality. You can depend on 
ADCOLA day after day. That's 
why they're so popular. You get 
consistent good service . . . relia- 
bility .. . from our famous therm- 
ally controlled ADCOLA Element 
and the tough steei construction 
of this ideal production tool. 

Write for 
price list 
and 

catalogue 
ADCOLA PRODUCTS LTD., 

(Dept. L ), ADCOLA HOUSE, GAUDEN RD., LONDON, S.W.4. 
Telephone: 0t-62Z 0291/3 ■ Telegrams: Soljoint London Telex .Telex: Adcola London 21851 




EX RENTAL TV's 



17 

SLIMLINE 
405 ONLY 

£11.10.0 




2 YEARS' GUARANTEE 

FREE ILLUSTRATED 
LIST OF TELEVISIONS 

17"— 19"— 31"— 23" 

WIDE RANGE OF MODELS 

SIZES AND PRICES 

DEMONSTRATIONS DAILY 

CARR. INS. 
30/- 



19 

SLIMLINE 
405/625 
BBC 2 
39 gns. 




RECORD PLAYER CABINET 
49/6 




Cloth covered. Size I6£" x t-4£" -> 
Takes any modern autochange 
P. & P, 7/6, 



TWO-YEAR GUARANTEED 
REGUNNED TUBES 




70° & 90' Mir.— WM, I7in.— 99,<6, 
21 in — 109:6. I 10- I7in.. I9in.&2lin. 
— 109/6. 2 J" (not bonded)— 129/6. 
Exchanged Bowls. Carr, 10 6. 



SPEAKERS GALORE. BRAND NEW 10 

15 tl, 4- (On, 3->S"BtJ,7">;4"and 6"x3' 3D. 



P. & P. 



2|"B!1, 3J' 



TRANSISTOR CASES, 4 FOR £1. Cloth covered, many colours. Size 
9±" -.'. 6±* x 3i". P. & P. 9/6. Similar cases in plastic. 

RECORD PLAYER* TAPE MOTORS 10 - BRAND NEW P. & P. 3 6. 



TRANSISTORS 2 6 EACH. 
AFII7, ACI28. 



OC4-4, OC4S, OC7I. OC6I, OCSID. API 14, 



DUKE & CO. (LONDON) LTD. 
621/3 Romford Road, Manor Park, E.12 

Phone Ot-473 6001-2-3 Sump for Free List 



£JL 



PRINTED CIRCUIT KIT 

BUILD 40 INTERESTING PROJECTS on 1 PRINTED CIRCUIT CHASSIS with 
PARTS and TRANSISTORS from your SPARES BOX 

CONTESTS: (1) 2 Copper Laminate Boards 41" X 21" . (SJ 1 Board lor Match- 
box Radio. {8] I Board for Wristwateh Radio, etc. (4) Bcsi.it. 15) Resist Solvent. 
(fi) Etchaut.(7) Cleanser/ Degreaser.iS) 16-page Booklet Printed CfKvrfti/or Amateun. 
(9) 2 Miniature Radio Dials SW/MW/1W. Also free with each kit. (10) Essential 
Design Data, Circuits, Chassis Plaits, etc, for 40 TRANSISTORISED PROJECTS. 
A very comprehensive selection oi circuits to suit everyone's requirements and 
constructional ability. Many recently developed very efficient designs published 
lor the first time, including 10 new circuits. 

EXPERIMENTER'S 
PRINTED CIRCUIT KIT 

8/6 

Postage * Pack. 1,6 (UK) 

Commonwealth ' 

SURFACE MAIL 61- 

A1K MAIL 8/- 

Austr&lia, New Zealand 

South Africa, Canada. 

1) Crystal Set with biased Detector. (2) Crystal Set with volt age -qn ad rupler 
detector. <3) Crystal Set with Dynamic Loudspeaker. (4) Crystal Tuner with Audio 
Amplifier. (5) Carrier Power Conversion Receiver. (6) Spill-Load Neutralised Double 
Reflex. (7) Matchbox or Photocell Radio. <S) "TRI-FLEXO.V Triple Reflex with 
self -ad jits ting regeneration (Patent Pending). (9) Solar Battery Loudspeaker Radio. 
The smallest 3 designs yet offered to the Home Constructor anywhere in the "Wot Id. 
3 Subminiature Radio Receivers based on the "Triflexon" circuit. Let US know 
it you know of a smaller design published anywhere. (10) Postage Stamp Radio. 
Siie only 1-62' x -95" x -2o*. (11) Wristwateh Radio 115* x -SO" x -Si". (12) 
Ring Radio -70' x -70' X -85". (13) Bacteria- powered Radio. Run* on sugar or 
bread. (14) Radio Control Tone Receiver. (15) Transistor P,'P Amplifier. (16) Inter- 
com. (17) 1-valve Amplifier. (IS) Reliable Burglar Alarm. (19) Light-Seeking Animal, 
(tabled Missile. (20) Perpetual Motion Machine. (21) Metal Detector. (22) Transistnr 
Tester. (23} Human Body Radiation Detector. (24) Man/Woman Discriminator. 
(25) Signal Injector. (26) Pocket Transceiver (Licence renulrcU). (27) Constant 
Volume Intercom. i'>Sj Remote Control of Models liv Induction. (29) Inductive -Loop 
Transmitter. (SO) Pocket Triple Keflex Radio. (31) Wristwateh Transmitter, Wire-less 
Microphone, (32) Rain Alarm. (33) Ultrasonic Switch/Alarm. (34) Stereo 
Preamplifier. (35) Quality Stereo Push-Full Amplifier, (36) LlKht-Bcam Telephone 
"Ph otophone", (37) Light -Beam Transmitter, (3S) Silent TV Sound Adaptor. (39) 
Ultrasonic Transmitter. (40) Thyristor Drill Speed Controller. 




YORK ELECTRICS 

335 BATTERSEA PARK ROAD, LONDON, S.W.I I 

1 fotafU, a brief dctcripUon and Photographs of nil Kits and alt 

o. Electronic and l'huf&vU-ctrir JhhoJtHl Axxcwbtrit. 




FANTASTIC 
LOW PRICES! 



Due to huge purchase these superb U.S.A. construction kits can be offered at 25°,,— 50% off recommended list 

prices. Absolutely complete with most detailed construction and operating books. Available from all branches 

or by mail order for 7 6 CARRIAGE AND PACKING on each kit. Two kits or more carr. free. 



KG-865 50 Watt Stereo Amplifier Kit 



bf.lv xe psatorbh 

All Silicon Trsnsisiori lor Stability, 
Cleaner Sound • Extremely Wide 
Power Bind width and Frequency 
Response • 50 W IRF Power Out- 
put* Specially Selected Low-Koiif 
Presmp Transistors* Two Printed 
Circuit Boards lor Fait Easy 
AmwmMy •Convenient Front-Pace I 
Stereo Headphone Jack«Teak- 
finished Extruded Aluminium Front 
Panel • Two a.c. Convenience Out- 
lets. 




Output: B»W I HP, i.ilf per channel; 141V 
continuous tine mm * Response : = idB, M la 
:in, i)00 Htm Output Impedances: 4 through IB ohms, 
plus stereo ktadpbona%JM Distortion: under <";,, 
nt 00 Hz and 7, (106 H: mi.eed t i I at rated poieer 
• Input Sensitiyitj: Magnetic Phono. SmT; 
Timer and Auxiliary, ■■""m'titower Reqnire- 
ment: -JM-HoOr, suite a.t. 
Recommended Lint Price *34,19.8: 24 OHS 
Assembled 89 OHS. Tt;ik Case IS Extra 



KG -625 Deluxe 6in Vacuum Tube Voltmeter Kit 



Huge Sin Meter Scale • Ranges: d.e. 0-th I 
1-3-a-IJ in r,u-a0e-t,-i00r full scale 

• Accuracy; 1% of full teak ratdin* 

• Input Resistance: ii.Vtt to i.ymV 

• Ranees: a.c. 9-I-&~5-H-6&-JH)-i0e 
l.SOSV full tealt. «-i-i-ll-41~!M-jlu - 
1, 409-1, HW V full senfeO Accuracy : 
--: -7 "<,* Frequency Reijionse: — >dB, ME? 
to XMtlz; ± IdR, 7fl//i to SMMe% Ohm- 
meter Ran (tea; »-i,noo-io,0»o ohm*; 
o-l-it)-ioo-).omt,vamtUtterr^ I'.Y U-l. 
Recommended Liet Price fc'J-l.lLMij 
18 OHS. Kf; WO u K(4 fi'Ja ( Win ne 
Ranges) iiut 4iln Skale: 9 J GMBL 




KG -375 A Deluxe Solid-State Auto Analyzer Kit 



Tunc. up nml traultlc-ihool any rar. perfoi 
actual raid tests 



IPs sereint testers 



■ do all thi. 



Set Engine Idle and Automatic Trsns- 
miiiinn Shift Points* Detect Condition ot 
Point Surfaces • Detect Dliirihutor Wear 

• Check Voltagre and Current Regulator! 

• Check Genera ton tor both Current and 
Voltage Output* Find Poor or Open Earth 
Circuital Detect Variation in Dwell Angle. 
Recommended List Price £t!3. IT.": 
IB OHS. AaaenMed Prloa 21 GHS, 




^— ^— "^-^ WHY NOT BUY THE PAIR? 

KG-371 Deluxe Solid- 
State Timing Light ■ 

Perform/litre sutpastet assembled units 
routing inueti more 

He I pi Set Ignition Timing • Check i Synchronisation ot Doable 
Breaker Arms*Cbecks tor Sticking Automatic Spark-Advance 
Mechanism • Check! Distributor Cam Wear*Bailt-in dc Power 
Supply •Reliable Solid-State Circuit* Your car gtTea More miles 
per gallon; Improved performance; Greater reliability. 
Recommended Lint Price £12.1 9. : 9 GHS. A vn ilnble taeembM 
Only. 




ALL SILICON TRANSISTORS 

The NEW KG-980 
Stereo FM Receiver 
Kit 

Designed to Satisfy the Most 
Critical Listener 

R.F. and I.F. Fanela Assembled and Aligned* Front Panel Stereo Headphone lack 
and Speaker Muting Switch* Full Control! Including Tape Monitor* SOW I.H.F. 
Output* Usable I.H.F. Seniitivily: '.'fr!'* Frequency Response; -■ Idit, lit) to 
I i.'i"'.'//?*Harmouic Distortion: less than 1-'.'";,*A.W. Suppression: mere than 
.'<<f.fi* Channel Separation: .jffdfi* Complementary Transformerless* Power 
Output; S0W Lit F ($S1? per channel}: t4W continuous sine >we% Frequency 
Response: — IdB. is to tOfiOOHz0¥owti Bandwidth: V>-:ojiOtiHzat 1% harmonic 
distonioii% Two R.F. Stages* Stereo indicator light. Recommended 

List Price tmj.19.ti: 39 OHS. Assembled 49 018. Teid; Case S OHS. Extr.% 




STAR ROAMER 5-Band Shortwave Receiver Kit 

Bandscread: electrical, cnUI/i-alei 

»-iM* Sensitivity: lOnV for 

I'ldB vignat-lo-noisc ratio%t,F. 

Bandwidth: Stffs tt iSdB down 

• Best Frequency : rartsWc, 

' i -'ikllz •Speaker : tin permanent 

magnet typt% Power Supply: 

fitted, transformer operated*} 

Headphone Output: ton- Impe- 

d -I i ■ ■■ e • Valve Complements: 

l-OBEG, 1-OHRG, 1-liAXi . 

t-GAEti or l-GAJlimtomt 

Requirements: iSO-SMY, ,~i9Hz 

n.c.; l J It' •Covers 200 to 400kHz and 5 5 0k Hi to 30MHz in S Band-switched 

Ranges •Superheterodyne Circuit includes controlled regenerative I.F. stage* A.V.C, 

reduces fading snd blasting; A.K.L. cuts noise to a minimum* Aerial Trimmer 

effectively peaks incomlnu signals lor best reception* Illuminated '•£" Meter: Large, 

Easy-to-Read 7; in Slide Rule Dial. 

Recunimended List Price £>]. 19.0: 1* GHS, itwrillllifll Price lfl OHS. 




100-in-1 Electronic Science Lab 

LOOK AT THE PROJECTS TOV CAS BUILD 

• Electronic Scale •Electronic Timer •Signal 
Generator* Hybrid light Meter * Signs! 
Injector*Morse Code Buzzer •Electronic Cat* 
Metronome* Code Fluiher*CW Monitor* 
Ohmmeter*BoAi Horn* Hybrid Radio* 
Hybrid Voice Relay* Air-powered Radio 

* Polarity Checker • Va 1 ye Checker . l_ 
I nc I u< les : • D u :t I H e:i< luet • I'hotoeu • 1 • 
K|ie.tker* Sttsicr • Acri.il • Trinaiators. 

Reosaaneaded Liet Frlcc tie.i?.0: 9: ohs. 




KG -640 20,000 ohms Volt VOM Kit 

Bid PROFE8KI0XAL SIZE 8S RAXVE MULTI. METER 

• A.C. Volts (12 Ranges): (i-i-is-ie-iv-nti-ioo-too-son- . 
lfi')i)-:!,<}0d-i,WJuV*l}.C,Vt,\U (IS Ranges]: 0-0S-1 e-s-f_ 
iti-io-so-: 1 a •) -4 ''in - sm- I, eoo-s, 000-4, 000 V * Output Voltsf I 
!8 Ranges;: 'J-.'-l-s-lO-iO-sO-lOO-ioermtUsiMtuitt <a I 
Ranges}: •i-l.H'»)-100fiOO ohmt-IO megs. Centre scales at J'.'.ll 
i.ioo and /•.•')A'n*D.C. Current (10 Ranges}: o-so-ieo-\n 
400-tiMfxA . >-h:-2iPJ-i»0mA. S-.K-*# Decibels (I8Ran-l| 
KM] : —li to -t-7,(*D.C. Senslthrtty: :Q,0>>0 ohms per i»» or t 
10. nnO ohms per roll ( function, of scale multiplier ticilet.) It 1 

• Frequency Response: :'<>//; to beyond imntz * Accuracy ; I 
d.e. 8%, n.c. 5%*T*St Leads: one red, one black , each 4Sin ions* Multiplier Resis- 
tor!: All 1% carbon jitm, — 

Recommended Lint Price Jtl0.10.«: 950H8. Aeecmblcd Price 12 OHS. 




mm tan 



We offer .yon fully tenallieetl polj-cater/mylnr nnd Standard Long Double 

F.V.C. tapes fit Identical quality hi-li, vide range 3in. 150(1. 2/3 Sin. 226ft. 8/9 3I». 300ft. if- 

recording chiiractcrint ice as top grade tap«s.<(ujill(v 4in. 300H. 4/8 4ln. 450tt. 5/8 4in. COOft. 8,'- 

eontrol luanufivctun'. Thev lire truly worth a leir 5in. 600ft. 7/8 &in. 900it. 10/S din. 1,200ft. 16/- 

ruore coppers than acetate, sub-standard, iointefl SJin. 000ft, 19/8 SJiii. I,200it.l8/- fiiln. l.HOOit.U/- 

• >r cheap import". TRV ONE ANT) PROVE IT Tin. l.'JOOft. li'B 7in. l.SWft. 18'fl tin. 'J. 400ft. 87- 
VOLEBELK. 
Postage I/- reel. Post free less 



M tlrrea ruas. QusJity and Trade enquiries invited, NOTE. Large tape Hocks at all branches. 



Triple 
4 in, 300ft. 18/- 
oin. l,8001t. 28/. 
5jln.'>,400Jt,84'- 
7In, 3,u00f(. 44- 

Qua<lruplc 
Win. 600ft. 8/8 



Stockists of Leak, Quad, Chapman, Goodman, Armstrong, Tripletone, Linear, Rodgers, Truvox, Ferrograph, Wharfedafe, etc., etc. 



TECHNICAL 
' TRADING 



All Meit Orders; — 

• ARUNDEL V.. , . 7 ,SS" ,,St " t 

• BRIGHTON %^^'i n " d 

• I nMlilMJ I ©Tottenham Court Road 
LUnUUn Tel. MUSeum 2639 

• PORTSMOUTH JgS?«3S»< 

• SOUTHAMPTON ?J?&2t™ 



PERSONAL CALLERS Welcomad at all 
Branches where there are targe Hi-Fi and 
Component stocks at the keenest prices 
including: 

GARRARD 1015 Autochanger* complete 
with GARRARD STEREO CARTRIDGE 
7} GNS. 

MAGNETIC CARTRIDGES Gold ring 800H 
7£ GNS. 

Shriro AT33 £7. 10.0 (Both Listed over £10) 



Practical Eicctronics October 1970 






753 



The 1970 edition ol Lasky's Audio-Tronics catalogue is available FREE on request. 
Packed with tOOO's of items (of Hie Radio and Hi-Fi enthusiast, Electronics 
Hobbyist, Servicemen and Communications Ham Covers every aspect of 
Hi-Fi (incljdlng Lasky's budget Stereo Systems and Package Deals), Tape 
recording and Audio accessories plus Lasky's amazing money saving 
vouchers worth over £25. SEND TODAY. Send your name, address and 2/- 
for post and inclusion of your name on our regular mailing list. 

This month's voucher worth SOj- 




THORN PYGMY PLUG-IN 

A compact pygmy relay on an 8-pin base with D.P.D.T. eoniacts 
rated to 10A. (Some type are 3 P.O.T, on an 11-pin base). 
RN TYPE Contacts Base 



21 5048 
235001 
215080 
305030 
205024 
215042 



D.P.D.T. 
D.P.D.T. 
D.P.D.T. 
3.P.D.T, 
D.P.D.T 
D.P.D.T. 
Others available ir 



pu 



8 p 
Spin 
11 pin 
8 pin 
B pin 
vlted Quantities 



Coil Voltage 

48V AC/ DC 

40V DC 

60V ACfDC 

SOV DC 

24V DC 

42V DC 



LASKY'S PRICE II '6 posts* 



nsMHiiimB- 



Lasky s ceo, cm, cm 

Exclusively made for us in 
U.S.A. Great Savings! 

Post Five for Ten for 

C60 — 7/6 1/- 33/- 21- 62/- 3/- 

C90- 12/6 1/- 56/- 2/- 116/- 3/- 

C120- 17/- 1/- 75/- 2/- 139/- 3/- 

Ll S.A. Cassette head cleaner, 10/6, Post 1/- 





skyrouer mkii 



COMMUNICATION 
RECEIVER 

A short wave receiver, eiclu- 
sive to Lasky's, at a real econ- 
omy price. Four valve line up 
using one each 6BF.6, 8BA6, 
6AV6 and 6AR5 valves, gives 
highly sensitive reception and 
powerful gain. Switch sel- 
ected SVV frequency range 
cover: 1-5 to 30MHj in three 
separate bandspread ranges 
and full AM medium wave- 
band cover In one range 550- 
I.eoOkHi. Reduction drivetuning with hair tine cursor. Controls include volume on/off 
BFO, Band selector. Power on indicator lamp. External antenna connecttor-s and 
mains fuse at rear. Internal speaker plus standard omm jack socket for phones on 
front. For 220/240V a.c. mains operation. Strong metal cabinet finished in grey 
crackle with anodised silver tront panel. Siie 9} is 5} « SJIn. Complete with mains 
lead and lull instructions. 

LASKY'S PRICE £ I3.13«Q F? 

This meter kit by TMK offers the unique opportunity of building a really first- 
class precision multimeter at a worthwhile saving in cost. The cabinet, movement 
and range selector mounted in position is supplied with lha meter scale. The 
highest Quality components and 1% tolerance resistors are used throughout. 
Supplied complete with full constructional, circuit and oporaling instructions. 

20,000 O.P.V. Multimeter. Features 
MfinFI 9(1(1 2" measurement ranges with mirror 

muutL £uu scale Larga 3 ... 2in meter , Fu ii 

scale accuracy: DCV and current: | 2%, ACV: | 3%, 
resistance „3%, Special 0-6V DC range for transistor 
circuit measurements. 
SPECIFICATION 

• DCV: O-O 6-6-30-1 20-600-1 ,200V at 20K/OPV. • ACV: 
O-6-3C-120-6O0-1.2D0Vat1OK/OPV. • DC Current: 0-0-6-6- 
600mA. • Resistance: 0-10K100K-IM-10M/ohms (58-580- 
5BK-58K at mid-scaie). • Capacitance: 0-002-O'2^F (AC 
6V range), • Decibels -20 to , 63d8, • Output: 05,iF 
blocking capacitor. Uses two 15V (U7 type) batteries. 
Black bskelite cabinet— Siie 5±'< H' l|ln. Complete with 
test leads. 

KIT PRICE ONLY 92/- 




M0DEL 5025 



50,000 O.P.V. FEATURING 
57 MEASUREMENT RANGES 

Uses an entirely new range selection mechanism which permits the use ol a really 

large meter in s more compact cabinet. The range selected is indicated on the 

meter face. High speed rotary range selection knob; polai ly reversal switch, 

shielded meter movement with overload proleciion circuit; Special pA Sftd mA 

measurement ranges. 

SPECIFICATION DCV: 0-0-25-2-5-10-50- 

250-1. 000 V at 2SK/OPV. 0-0-1 25-1 -25-5-0-25- 

125-500V at 50K/OPV. ACV: 0-3-10-50-250- 

1,000V at 2-5K/OPV. 0-1 -5-5-25-1 25-500 V 

at 5K/OPV. DC/iA: 0-25;iA at 125mA: 

0-50fiA at 250mA. DCmA: 0-2- 5-25-250 m A 

at 125m V; O-5-50-500mA at 250m V DC 

Amps: 0-5A at 125mV; 0-10A at 250mV 

Resistance: 0-10M/ohms. Output: Capacitor 

(0-1 |iF. 400Vw) m series with ACV ranges. 

Decibels; - 20 lo 81-5dB. Operates on two 

15V baits Black bakelite cabinet, size 

5 T ■ 6J-- 2i'\n. Complete with test leads. 



KIT £10.10.0 




Posts/ 



ALSO AVAILABLE READY BUILT AND TESTED £12.10.0 Post 5- 



TMI & 
TM5 



MODEL TM-1 

The first of Lasky's new-look top value melers. the 
TM-1 is a really liny pocket multimeter providing 
"big ' meter accuracy and performance Precisian 
movement calibrated lo 3 , of full scale. Click 
stop range selection switch. Beautifully designed 
and made impact resistant black case— with while 
and metallic red/green figuring . Ohms zero. 

• DC/V: 0-10-50-250-1,000 at 1K OPV 

• AC/V: 0-10-60-250-1,000 at IK OPV, 

• DC CURRENT: 0-1mA, 100mA. 

• Resistance: 0-150M.V 

• Decibels: - 10<1B to 22dB 

• Complete with lest leads, battery and i 
lions. • 



77W-5 



LASKY'S PRICE 




POST 2/6 




Another new look pocket multi-meler from Lasky's 
providing lop quality and value. The "slimline" 
impact resistant case — size 4jin '* 2iin ■. t^in, 
fitted with extra large 2Jin square meter. Read- 
ability is superior on all low ranges: making this an 
excellent instrument for servicing transistorised 
equipment. Recessed click stop selection switch. 
Ohms zero adjustment. Buff finish with crystal 
clear meter cover. 

• OC/V: 3-1 5-1 50-300-1, ZOO at 5K OPV. 

• AC/V: 6-30-300-600 at 2-5K OPV, 
" DC Current 0-300;tA, 0-300mA. 

Resistance: 0-1QkQ, 0-1Mn. 
Decibels: 10dBto16dB. 
Complete with test leads, battery and instruc- 
tions. 



LASKY'S PRICE 49/6 



POST 2 6 



&Jv%&/vd 



SL-55 

OTHER GARRARD UNITS FROM 
STOCK 

AUTOCHANGERS M^L.^V7^^^^| 

SL7ZB fl^^^^^H^^P^i 

2025TC with stereo cartridge £1 17 6 
3000 complete with STAHC Jtereo 

cartridge £9 19 6 SFECfAL < 

SL65B £15 10 9 OFFER Ot"0» 

-. fl -D *■« n n One of the famous Garrard Synchro- 

ilU95B *"" * " Lab Series. Takes 8 LPs Four- 

SL75B £28 speed auto-changer; incorporating a 

SINGLE PLAYERS tubular pickup arm and adjustable 

„c , c rtetnn jio-jK..,:.h anTRK stylus force. Wired tor Mono and Stereo. 

AP 75 £18.10.0. AP75 with AD76K N £ w AT LASKrs SPEC | A L PRICE. 

mag. cart.. £21.10.0. 401 Transcription Complete with SONOTONE 9TA 
Umt£2000 STEREO CARTRIDGE. £10.19,6 

BASES AND COVERS FOR GARRARD UNITS 

Typr WB1 and WB5 for models AT60 Mk II. 202 5 TC. 3000, 5L6SB.5L55. 1025, SP25 
Mk. II. Price WB1 £3 16 6. WB5 £5 12 6. Type WB« for models SL72B ;. |L75B. 
SL95B Price £5 12 6. Perspex covers: SPC1 lor WB1 £3 14 1. SPC4 for WB4 and 
WB5 (allows unit to be play ed with the cover in place— Price £4 




754 



Practical Electronics October 1970 



SCOOPMT-65 special offer 



EXCLUSIVE HI-FI STEREO TUNER AMP. OFFER 
THE MT-65 CHASSIS 



Solrd slftle AM/FM multiple! tuner with FET front-enrj/17 17 wat;s stereo amplifier by world 
famous manufacturer. Frequency response 2Q-45KHz. Inputs— 2 3m V mag, p/u and 140mV 
tape play. Tape record output. Controls: Left/right volume, bass, treble, loudness, monitor 
Tuning meter and stereo heacon. Stereo 'phone jack. Machined stainless steel front panel 
Overall size 20x3$ xlSin. List Price £75. 



SPECIAL PRICE £66.0.0 



DE-LUXE "COMPACT" PACKAGE OFFER 

PTT-65 Chiuil £75 q q 

GARRARD AP-7S 1-ipeed Single P\i r tr £1] l< 7 

AUDIO DEVELOPMENT AD-96K Mijneiic Ciriridje iS iB t 

1WHARFEDALE DENTON Speiktr Syjiemi fj« 

"Compact" T«k Cabinet (w shown) £7 10 

TOTAL RECOMMENDED LIST PRICE £148, S.I 



LASKY'S 

PACKAGE 

PRICE 




£132.0.0 



UK.; carriage 40/-. 

All units available separately 



Project 




Profact 14 it ■ rang* of modulai which connect tog.thar to lorm • compitia it«reo 
ampllflar. Tha modulai ara: 1. Z-3TJ hloh gain power amp. 2. Slarao-M pre-amp 
control unit. 3, Tha P2-5 unitablllaad and PZ-f itabllliad powar lupplla* A compiata 
• yitam comprint two Z-3C 1. ona Starao-tt and a PZ-S or PZ4, 

STIREO BO SPECIFICATION 

Input sensitivities: Radio up to 3mV, Magnetic Pick-up 3nW: correct 10 P, I A A curve 
:1rJB; 20 to 2S.D0OHZ. Ceramic Pick-up up to 3mV 
Auxiliary up to 3mV *) Output 1 volt • Signal to noise: 
better man 70dS Front panel: brushed aluminium 
with black knobs and controls # Size SVt * 1v» x 4in. 



£9.19.6 



post as 
Z-30 SPECIFICATION 

# Power ouipul 15 w. R. M.S. into B ohms using a 35 volt supply • Freq uency response 
30 to 300.000Hz * 1dB # Distortion: 02% # Signal to noise: better Thar 70dB £ Input 
sensitivity 250mV into 100 K ohms • Loudspeaker imp: 
3 to 15 ohms a) Power requirements: from 8 to 35 V DC 

{The Z30 will operate from batteries if required} - 
Size: 3V, x 2W 

PZ5 
PZ6 



,< 89 6 

30V unstabilised — sufficient to drive two 

2-30's and a Stereo 60 for domestic nM ,— 

applications. 99 / O 

35V stabilised — ideal lor driving two 

Z-30's and a Stereo 60 lor low efficiency 

Speakers. 



£7.19.6 post 2/6 
PACKAGE PRICE ^.trygnfpz'y jB20.0.0 .> p os , » 

litH:lil!H f 

MAGNETIC RECORDING TAPE FROM THE U.S A 
AT LASKY'S RECORD LOW PRICES 



Message tape, 150ft 2 I 

Message tape, 225ft 3 t 

3in. Message tape. 300ft Ti 

avkin. Triple play. SOOfi Mylar 10 

Sin. Double play, 1200ft is 

iin Long play. SOOtt Acetate ,, 10 

5in, Slandard play 600ft. If 

5**in Double play, 1800ft. Mylar 22 

5Win. Long play 1200ft. Acetate 15 

SWin. Standard play 9O0ft. PVC ... 12 S 

P. 1 P. I,'- extra par real. * r.eli and aver 



in. Long play. 1200ft Mylar... 15 

in. Triple play. 2«00ft 350 

Standard play. 1200ft. 

Acetate 12 f 

Standard play. 1200ft. 

Mytar 12 S 

Long play, 1800ft Mylar.... 10 « 

Double play, 2*00f- Mylar 25 

Long plat 1000ft. Acetate.. 15 

Triple play 3600ft Mylar .... 50 

Free. So.clnl duoi.i for Quantities. 



Bgpg 



DIGITAL CLOCK 
SCOOP! 




• SHOCK AND 
VIBRATION 
PROOF 

• BUILT IN 
ALARM 
BUZZER 



MADE ESPECIALLY 
FOR LASKY'S BY 
FAMOUS MAKER 
MAINS OPERATION 
12 HOUR ALARM 
AUTO "SLEEP" 
SWITCH 

HOURS, MINUTES 

AND SECONDS 
READ-OFF 
FORWARD AND 
BACKWARD TIME 
ADJUSTMENT 
SILENT OPERATION 
SYNCHRONOUS 
MOTOR 



SPECIAL QUOTATIONS 

FOR QUANTITIES 

This unique DIGITAL CLOCK is now available EXCLUStVELY FROM 
LASKY'S in chassis form for you to mount in any housing that you choose, 

All settings are achieved by two dual-concentric controls at the front Including.' 
ON-OFF-AUTO and AUTO ALARM, "sleep" switch, 10 minute division "click" 
set alarm {up to 12 hour delay), time adjustment. Ultra simple mechanism and 
high quality manufacture guarantee reliable operation and long life. 
The sleep switch will automatically turn off any appliance— radio, TV, light, etc., 
at any pre-set time up lo 60 mlr, and in conjunction with the AUTO setting will 
switch on the appliance again next morning. 

The clock measures ■SjWx 1jMHx3|D (overall from front of drum to back of 
switch). SPEC: 210/240V AC, 50H* operation; switch rating 250V, 3A. Com- 
plete with instructions. HUNDREDS OF APPLICATIONS. 
COMPLETE WITH KNOBS. 

LASKY'S PRICE £6.19.6 -«*> 

'.ilU.H.IiU'JJfllJi'.l:^ 

AD-309K 

PRECISION PICK-UP ARM 
COMPLETE WITH AD-76K 
MAGNETIC 

CARTRIDGE 




balanced pick- 
eted with the 
outstanding 
AD-76K magnetic 
cinridjt is constructed of br«s throughout, heavily chrome- 

needfe and mimau-e ba.fi race bearing*; both 
coarse and fine balance adjustment is provided. The fixed head 
hat standard jin. mounting centres and is finished in black enamel 
with chrome lifting spur. Completely wired, with all fixing nuts and washers. Arm rest 
atso suppfred. Tech. details? Overall length 285mm ; needfe to pivot length 223mm 



'f*t 



angle 24 



rhinf I0mm h Requires single 7; 16m, di: 



; hole 



LASKY'S PRICE £9.19.6 

m 



207 EDGWARE ROAD. LONDON. W.2. Tel; 01 -723 3271 

33 TOTTENHAM CT.RD, LONDON. W1P 9R8. Tel: 01636 2BD5 



109 FLEET STREET, LONDON, EX.4. 
152/3 FLEET STREET, LONDON, E.G.4. 



Tel: 01 -353 5812 
Tel: 01-353 2833 



HIGH FIDELITY AUDIO CENTRES 

42-45 TOTTENHAM CT. RO, LONDON, W1P 3RD. Tel: 01-580 2573 



118 EDGWARE R0A0, LONDON, W.2. 



Tel: 01-723 9789 



tlfte 



ALL MAIL ORDERS AND CORRESPONDENCE TO: 3-15 CAVELL STREET, TOWER HAMLETS, LONDON, El 2BN Tel: 01-790 4821 



Practical Electronics October 1970 



755 



BRAND NEW FULLY GUARANTEED TRANSISTORS 

¥o N R D NEW LIST • NEW PRICES 



1X4001 

1X400-2 

1N400U 

1X4004 

1X4005 

1X400S 

1X4007 

1X4003 

IN4MS 

•2G210 

2G240 

2G301 

2G302 

2G303 

2G308 

i>G3u8 

-2G309 

■2G371 

2G374- 

2G381 

2G382 

2G383 

2K404 

2X696 

2X0 9 7 

2X69H 

'JX70B 

■2X7 OCA 

2X707 

2X708 

2X914 

2X910 

2X918 

2N919 

2X920 

2X922 

2X930 

2H1131 

2K1303 
2X1304 
2X1305 
2X1306 
2X1307 
2X1308 
2X130W 
2X1613 
2X2147 
2X216(1 
JS2287 
2X2046 
2X2904 
2X2900 
2X2625 
2X2926 
2N301 1 
2X3053 
2X3054 
2X3055 
2 N" 3702 
•2X3703 
2X3704 
2X3705 
2X3707 
2X3709 
2X3710 
2X3711 
2X3730 
■2X3731 
2X3794 
2X3819 
2N3820 
2N3S23 
2X406S 
2X4061 
2X4286 
2X4288 
2X4289 
2X4290 
2X4291 
2X4292 
40361 
40362 
2S001 
2S002 
2S003 
28004 
2S005 
28012 
2S013 
2S017 
2S034 
2S036 
28320 
2S321 
2S322 
2S323 
28324 
2SSJ2 
2S701 
2S702 
2S731 
2S732 
23733 
AA178 
AAY 12 



l/« 

i e 
a 

8 - 
2 I 

a - 

Is 
1 1 

;o 
■is 6 

4.. 

48 

S- 

B; 

6- 

jfc 

46 
5 6 
5 

6 
5 

4 
K 

KC 

e/e 

& 

2 a 

9 6 
| 

4 8 

4 e 

7 
4 

5 - 

8 G 

Sh 

»■• 
i- 

4 8 

5 - 
j 

5/- 

6/- 

91- 

6, 

46 

13,'6 
85. 

10/8 

91- 
7/8 

m 

28 

5 

5/ 

10 

16/- 
2 6 
8/6 
3,8 
3/6 

a/- 

2/8 
2/8 

m 

10 
12/ 
2 3 
71- 
17/8 
17/6 
3/8 
V- 
»/- 
3/- 
3/6 
3<- 
91- 
3/- 
11/- 
18;- 
10/- 
10/8 
8/8 
0/3 
If 
25. 



\AZV2 4- 

AAS513 2/8 

AAZ17 2/- 

AC12G S/- 

AC127 57- 

AC127Z 10.'- 

AC12S 5.'- 



16/- 
18/6 

»;■ 
u 

6/. 
7 8 

10/ 

18/8 
9/6 
8/8 

11/- 
8/3 
8/6 
8/6 
86 
5/- 



AC153 
AC 164 
AC 169 
AC176 
AC 187 
AC188 
ACY17 
ACY18 
ACV1& 
ACY20 
ACY21 
ACT22 
ACY2S 
ACY34 
ACT 36 
ACY39 
ACY40 
AD140 
AD149 
AD161 
AD162 
AF102 
AF114 

AFU5 

AF116 

AF117 

AFI18 

AF124 

AF126 

AF126 

AF127 

AF139 

AF178 

AF181 

AF186 

AF239 

AFY19 

AFZ11 

AFZ12 

ASY2-, 

ASY27 

ASY28 

A*Y2!.' 

ASYC7 

Ajazsi 

AUY10 

B3M 

BA110 

BAY31 

BC107 

BC108 

BC109 

BC113 

BCllfi 

B01I8 

1SC134 

BC135 

BC136 

BC137 

BC13S 

BCY30 

BCY31 

BCY33 

BCY33 

fit" Y 34 

l« Y38 

lit- VMS* 

11CY40 

ltCY-i-J 

BCY43 

RCY70 

BCZ11 

BC147 

BC148 

BC149 

BF152 

BF194 

BF195 

BD124 

BEX3000 5 

BF11S 5 

BF154 

BF1B8 

BF159 

BF163 

BF167 

BF173 

B7180 

BF1S1 

BFX30 

BFX88 

U1-V20 

BFYBO 
BFYS1 
BFYGS 
BFYSS 

BFYIS4 
BLY10 
BLY 1 1 



4- 
3 

3 - 
61- 

i- 

8;- 
&■- 

4:- 

5 

4 - 

4 8 
3 6 

5 6 
4 
5, 

11 

3 

10 - 
10/ 

7/6 

7 6 
12 6 

5 1 
8 

6 6 
5 - 

It 8 
8/ 
5 

4/- 
4,1- 
6/- 
9/6 
8/8 
8/- 
»!- 
338 
12 6 
15 - 
5/- 

7 6 
6/- 
B/- 
6/8 
8/8 

19/6 
19/8 
87- 
2- 
2.8 
S/6 
2.8 
6/ 
8'.'- 
7,'B 
7/8 
6/- 

7;- 

8, 
8, 

5,8 
8/- 
10/- 
*!- 
51- 
W- 
8/8 
8/8 
S/- 
9h 
4/- 
7-6 
3/9 

2 9 
4/- 
91- 

3 5 
91- 

12/6 



BFY10 
BBX80 

BSX21 
BSX7C 

BSY27 

BSY28 

B8Y29 

BSY50 

B8Y03 

BSY66 

BSY67 

BSYWA 

BSY90 

BY 100 

BY 108 

1JYVJ6 

BY 127 

BYZ10 

BYZ1 1 

BYZ12 

BYZ13 

BYZ15 

BYZ19 

GET 102 

GKT103 

MPF102 

MFF103 

MFF104 

MFF10I) 

0A6 

0A7 

0A» 

OA10 

OA47 

OA70 

0A71 

OA73 

OA74 

OA79 

0AB1 

OA85 

OA88 

OA90 

0A91 

0A9S 

OA200 

OA202 

OA210 

0A211 

OAZ225 

OAZ228 

OAZ22tt 

OAZ231 

OAZ234 

OAZ23M 

0C16 

OC19 

OC20 

0G22 

DOSS 

OC24 

OC26 

0C2H 

OC28 

OC29 

0C3S 

OC36 

0C41 

0C42 

0C43 

Of44 

OC46 

OC4U 

OC70 

0C71 

OG72 

OC73 

OC74 

OC75 

OC76 

OC77 

OC78 

0C81 

Ot'8 1 1) 

OC82 

0CS8 

OC84 

OC122 

00 ISO 

0C131I 

OC140 

0C141 

W.:i69 

OC170 

OC171 

OC200 

OC201 

©(.■■^fi'J 

OC203 

OC204 

0C2 116 

oca OB 

OC207 
OC'1'7 1 
ORP12 

OKI"-.'; 



2N30SS 15/- 

MuMard I 15 wntt 

Silicon Power 

25 + 13/- 

100 + U/- 



NTEGRATED CIRCUITS 

Type I 12+ 25+ I00 + S00 + 

UL9I4 919 91- 9/- 7/1 6/6 

UL923 12/6 It/9 1 1/- 10/- 9/J 

SL403A 42/6 41/- 40/- 37/6 35/- 

MC1303 5J/6 48/ 45/- 40/- 35/- 

MC1304 55/- 50/- 47/6 42/6 37/6 

PA246 51/6 48/- 45/- 40/- 35/- 



2N2924 2/6 

NPN Planar 

All Colours 

25 + 1/8 

1O0 + 1/6 



|AF13? 6/- 

Siemens V.H.F. 
25 + 5/3 

1 00 + 4/6 
500 + 3/9 



5 - 

2 

I 

tl 

i 

Zh 

2- 
2 - 
26 
4 

2 - 
1 6 
1 6 
1 6 
2- 
o 

7.6 
7 6 
7 6 
9 I 
9 G 

7 6 

3 9 

8 8 
7 6 

19 6 

9 I! 
10 
10- 

S 8 

i 

12-8 
12 6 
l« 
12 6 

5 - 

6 

B 

4, 

3 8 

5 8 

919 

3/ 

5/ 

i 

6/ 
Sl- 
it 
8- 

er- 

91- 
4/- 
5/- 
S/- 

&l- 

10/- 

10/- 
6/- 
7/6 

18/- 
4 
6 

6/- 
7 6 
9.6 

12/8 
7/8 
91- 

12/8 

15/- 

16/ 

19 

11 
8 



OBI70 

25 + 4/3 
100 + 3/6 



OC17I 

25 + 5/3 
1 00 + 4/6 



BYI27 4j- 

Mullard lOOOv 

I amp Plastic 

25 + 1/1 

100 + 1/- 



2N38I9 7/- 

Texas F.E.T, 
25 + 6/- 
100 -I- 5/1 

500 + 4/9 



2N2646 10/6 

Motorola 

Unijunction 
25 + 8/9 
100 + 7/6 
500 + 6/9 



AF186 91- 

Mullard V.H.F. 
25 + 7/- 
1 00 + 6/- 
500 + 5/- 



BY 126 3»- 


Mullard 800 v 


1 amp Plastic 


25 +2/6 


100 + 2/3 


BY2Tb XI 


Milliard 6a 200 v 


25 + 1/6 


100 + 1/2 


500 +2/10 



BTI02.S0OR 15/- 

Mullard Thyristor 

500 p.i.v, 6-5a 

25 + I J/6 

100 + 11/- 



OA200 OA202 

1/9 

SILICON Diodes 
25 + 1/6 
100 + 1/3 
500 + l/l 



OC42 

Mullard 
25 + 5/3 
100 + 4/9 
500 + 4/3 



§/• 



OC45 

Mullard 
25 + 3/- 
100 + 1/6 

500 + 2/- 



3.6 



OC75 

Mullard 
25 + 4/3 
100 + 3/6 
500 + 3/- 



OC20 19/4 

Mullard lOOv 
25 + 15/9 
100 + 14/6 
500 + 13/3 



N 4004/5 2/6 

400-SOOv t amp 
25 + II- 
100 + 1/9 
500 + 1/6 



BCI07 8.9 2 6 ea 

I.T.T. Planarj 

25 + 1/1 

100 + 1/- 

500 + 1/9 



OCP7I 19/6 

Mullard Photo 
25 + 17/3 
ICO + 14/9 
500 + 13/6 



OC28 12/6 

Mullard Power 
25 + 11/- 
100 + 10/- 
500 + 8/6 



OCT I 

Mullard 

25 + 1/3 
100 + 2/- 
500+1/9 



V 



BCY34 

Mullard 

25 + 4/1 
100 + 1/9 
500 + 3/6 



N400I/2/3 1/6 

I amp I00-300v 
25 + 1/4 
100 + 1/2 
500 + 1/- 



IN4006/7 3/- 

800-IOOOv I amp 

25 + 1/10 

1 00 + 1/6 

5O0 + 2/3 



OCI39 

Mullard 
25 + 41- 
100 + 3/3 
500 4- 3'- 



5 



ZENER 

DIODES 

4O0 MW 5% 
BZY88 Range 
All Voltages 

3-3v-33v 3/6 
25 +2/9 
1 00 + 1/- 
500+1/9 
1000 + 1/7 
any one type 



OC140 

Mullard 
25 + 61- 

1 00 + 5/- 
500 + 41- 



7/6 



PLEASE NOTE MINIMUM OR D ER SHOULD BE 10- 

Quantity prices 100+ Phone <0l) 723 NEW A UTUMN ..LIST. NJEW 
040.E..4. AM listed devices are from """SjNEW PR.CK.ASK FOR 
stock at time of going to press. Please TODAY. Discounts 10% on 12 + any 
add 1/6 post packing to your order. one type. 15% on 25 + any one t ype 



303 EOGWARE ROAD 
LONDON. VV.2 

(01) 72 3 1008;° 

OPEN MON-SAT 9am-6pm THUBS vjm-lpm 




PRINTED CIRCUIT BOARDS for P.E. PROJECTS 




All bontfle .Iriilt'd and roller t iimd 


nrllipk't 


• with layou 


dra-ninp. 




Some ol the moot papular boards .1 


rt listed lietow: 






June 1968 


Light Operated 




Auk. 1969 


Spring Line Reverb 


16/8 




Otnerii Trigger 


3/10 


Oct. 1969 


Audio Signal Genera- 




Julv IMS 


Drill Speed Control 


4/8 




toc 


8/6 


Dec. 196S 


Door Chimes 


*/8 


Kov. low 


l.C. Hsuilc Awplllier 


8/- 


Dec. 1968 


Stock Mttrket Buttle j 


3- 


Not. 1969 


I-C, Stereo Amp. 


ie/e 




Central Exchange 


6- 


Uee. 1969 


HI-FI Stereo 


86 8 


Jan. 1969 


Stabilised Power 




!>«■. 1969 


Doable Sis Main 






Supplv. 3 boartls 


16/6 




Circnlt 


10 - 


Feb. I960 


Hiirmoiiophone 


8/- 


Jan. 1970 


HI-FI Stereo Pro- 




Feb. 1969 


Electric Fencer 


e/- 






£2 6 


Mat, 1969 


Fhotographic Timer 


78 






S/- 


Mar. 1 969 


Mo dern A ud io C i reti 1 1* 


* .- 


June 19T0 


found Trigger 


4/e 


Apr. 1969 


Microphone Mixer 


18/- 


June 197(1 


D.c. Multimeter: 




June 1970 


Model Train Control 


8/- 








Apr. 1969 


Interrupted Rcreen- 






StHbilleer 






wlper 


5/4 


Jum- 19^6 


Flashing Light Show : 




June 19*59 


Linear Scale Ohm- 






Monoa table Panel 


7.'6 




meter 


8.8 




Diode Panel 


6- 


b\A.E. lor list. No« available frui 


i: Henry 


■ Radio Ltd. 


Edgirftre R'l., L*»n<l'>n 


W.2. 


p.H. ELECTRONICS, Industrial Estate, Sandwich, Kent 






for fast, easy, 
reliable soldering 

Contains 5 cores of non-corrosive 

flux, instantly cleaning heavily 
oxidised surfaces. No extra flux 
required. 



SAVBIT ALLOY 
ALSO REDUCES 
COPPER BIT WEAR. 

Ecomicaliy packed for 

general electrical 
and electronic 
soldering. 75 ft. 
16 gauge on 
plastic reel. 
Recommended 
retail price 15/- 




A RANGE OF 
SOLDERS IN HANDY 
DISPENSERS. 



REF, ALLOY SWG 



4 A 60/40 18 1- 
SizeS 
X;. Savblt 18 3/- 

ted) 
15 60/40 22 4/- 

•Recomniended Price 



THIN GAUGE 
SOLDER, 
ESSENTIAL FOR 

soldering small components 
and thin wires. High tin 
content, low 
melting point, 
60/40 alloy, 170 ft 
22 gauge on 
plastic reel. 
Recommended 
retail price 15/- 




INVALUABLE FOR STRIPPING 
FLEX, THE NEW AUTOMATIC 
OPENING BIB WIRE STRIPPER 
AND CUTTER, easily 

adjustable for all 
standard 

diameters. Plastic 
covered handles 
can also be used 
as wire cutter. 
Recommended 
.retail price 8/6 




i From Electrical and Hardware shops. If unobtainable, writ! 
<$§> Multicore Solders Ltd., Hemel Hempstead, Herts. 




AMAZING MINI-DRILL 



FOR 
PRECISION 

MODEL 
WORK 




+ 6 TOOLS 



Indispensable for precision 
drilling, grinding, polishing, 
etching, gouging, shaping. 
Precision power for the 
enthusiast. Shockproof. 
Completely portable power 
from 4J- volt external 
battery. So much more 
scope with MINI-DRILL. 
Super Kit (extra power, in- 
terchangeable chuck) 79/6 
p.p. 2/6. 

De Luxe Professional Kit 
with 17 tools 130/- p.p. 
4/6. 
Money Ref. Guarantee, 



756 



MERLIN SUPPLYCO 



Dept. PEIOD.Nailsea, Bristol SSI? ZLP 



Practical Electronics October 1970 




MONOLITHIC 
INTEGRATED CIRCUIT 
AMPLIFIER AND PRE-AMP 




theworld's most advanced high fidelity amplifier 



The Sinclair IC-10 is the world's first monolithic integrated circuit 
high fidelity power amplifier and pre-amplifier. The circuit itself, a 
chip of silicon only a twentieth of an inch square by a hundredth of an 
inch thick, has an output 5 watts R.M.S. (10 watts peak). It contains 
13 transistors (including two power types), 2 diodes, 1 Zener diode 
and 18 resistors, formed simultaneously in the silicon by a series of 
diffusions. The chip is encapsulated in a solid plastic package which 
holds the metal heat sink and connecting pins. This exciting device 
is not only more rugged and reliable than any previous amplifier, it 
also has considerable performance advantages. The most important 
are complete freedom from thermal runaway due to the close thermal 
coupling between the output transistors and the bias diodes and 
very low level of distortion. 

The IC-'IO is primarily intended as a full performance high fidelity 
power and pre-amplifier, for which application it only requires the 
addition of such components as tone and volume controls and a 
battery or mains power supply. However, it is so designed that it 
may be used simply in many other applications including car radios, 
electronic organs, servo amplifiers (it is d.c. coupled throughout) etc. 
The photographic masks required as part of the process of producing 
monolithic I.Cs are expensive but once made, the circuits can be 
produced with complete uniformity and at very low cost. This enables 
us to cover every IC-10 with the Sinclair guarantee of reliability. 



■ SPECIFICATIONS 

Output 10 Watts peak, 5 Watts R.M.S. continuous. 

Frequency response 5 Hz to 100 KHz±1dB. 

Total harmonic distortion Less than 1% at full output. 
Load impedance 3 to 1 5 ohms. 

Power gain 1 10dB (100,000,000,000 times) total. 

Supply voltage 8 to 1 8 volts. 

Size 1 x 0.4 x 0.2 inches. 

Sensitivity 5mV. 

Input impedance Adjustable externally up to 

2.5 M ohms. 

■ CIRCUIT DESCRIPTION 

The first three transistors are used in the pre-ampand the 
remaining 10 in the power amplifier. Class AB output is 
used with closely controlled quiescent current which is 
independent of temperature. Generous negative feed- 
back is used round both sections and the amplifier is 
completely free from crossover distortion at all supply 
voltages, making battery operation eminently satis- 
factory. 

■ APPLICATIONS 

Each IC-10 is sold with a very comprehensive manual 
giving circuit and wiring diagrams for a large-number of 
applications in addition to high fidelity. These include 
stabilised power supplies, oscillators, etc. The pre-amp 
section can be used as an R.F. or I.F. amplifier without 
any additional transistors. 



SINCLAIR 
I W i I U manual «J %J ' 6 

POST FREE 







Practical Elecironics October 1970 



SINCLAIR RADIONICS LIMITED 
22 NEWMARKET ROAD CAMBRIDGE 

Tel. 0223 52731 



757 







Project 60 




Laboratory standard modular high fidelity 

Sinclair Project SO comprises a range of modules which connect together simply to form a f^^^^!^^S^hS^S& 
performance. So good, in fact, that only 2 or 3 amplifiers in the world can compare in overall performance and now the constructor has choice 
of assemblies with either 20 or 40 watts output per channel, with or without filter f « llltie f ■ . „_*„, lttM 3 The Active Filter Unit. 

The modules are- 1. The Z.30 and Z.50 high gain power amplifiers. 2. The Stereo 60 preamplifier and control unit. 3. The Active ruwr urm. 
4 4 Juook unfts-PZ 5 PZ 6 PZ 7 and PZ.8. In a normal domestic application, there will be no significant difference between PZ.5 o PZ 6 
unUs loXeLrs , of very i low efficiency are being used, in which case the PZ 6 will be required. J^^^^S^'iSSp^ 
PZ.8 supply unitto ensure maximum performance from these amp Iflers. No skill or experience »™ «"f£ * b "; ld J X svstemls that U s nSt 
60 manual gives all the Instructions you can possibly want, clearly and concisely. Perhaps .the greatest .beauty of ^ he system ' s that '* IS "a 
only flexible now but will remain so in the future as new additions are made to the ra nge. A stereo F.M. tuner is next to come, i nese ana ail 
other modules introduced will be | \ , n „„ nil ,„„*!„,, with ^JX*" 



compatible with those already 
available and may be added to 
your system at any time. And 
because Sinclair are the largest 
producers of constructor modules 
in Europe, Project 60 prices are 
remarkably low. 



System 



The Units to use In conjunction with 



Car Radio 



Z.30 



Existing car radio, Sinclair 
Micromatic 



89/6 



Simple battery powered 
record player 



Z.30 



Crystal pick-up, 12 V or 

more battery supply and 

volume control 



89/6 



Mains powered record 

player 



Z.30 and PZ.5 



Crystal or ceramic P.U. 
Vol. control etc. 



£9.9.0 



20 + 20 watts RMS 

stereo amplifier for 
most needs 



Two Z.30s, 

Stereo 60 and 

PZ.5 



Crystal, ceramic or magnetic 

P.U., most dynamic speakers, 

FM tuner, etc. 



£23.18.0 



20 + 20 watts RMS 

stereo amplifier for use 

with low efficiency {high 

performance) speakers 



Two Z.30s, 

Stereo 60 and 

PZ.8 



High quality ceramic or 

mag, P.U., F.M. Tuner, 

Tape Deck, etc. 

All dynamic spkrs. 



£26.18.0 



2 



How to assemble and use Project 
60 modules to best advantage in 
the above and other applications 
will be found in the fully descrip- 
tive 48-page Project 60 manual 
included with Project 60 systems. 
Available separately, price 2/6d 
including postage. 



40+40 watts RMS de- 
luxe stereo amplifier 



Two Z.SOs, Stereo 

60 PZ.8 and mains 

transformer 



As for E 



£32.17.6 



Outdoor public 
address system 



Z.60 



Microphone, up to 4 P.A, 

speakers, 1 2V car battery 

with or without converter, 

controls 



£5.9.6 



Indoor P.A 



One Z.50, PZ.8 

and mains 
transformer 



Mic, guitar, heavy duty 
speakers etc., controls 



£17.8.6 



High pass and low 
pass filters 



AFU 



D, E or F as above 



£5.19.6 




To be released shortly 



—I 



SINCLAIR RADIONICS LIMITED 

22 NEWMARKET ROAD, CAMBRIDGE Tel. 0223 5273 1 



758 



Practical Electronics October 1970 




- AN- 



tj 



^1 in^H HP 





GUARANTEE 

If within 3 months of purchasing Project 60 modules directly 
from us, you are dissatisfied with them, we will refund your 
money it once. Each module is guaranteed to work perfectly 
and should any defect arise in normal use we will service it at 
once and without any cost to you whatsoever provided that 
it is returned to us within 2 years of the purchase date. There 
will be a small charge for service thereafter. No charge for 
postage by surface mail. Air-mail charged at cost. 

inrfsir- 



Z.30 & Z.50 1WS 



AMPLIFIERS 



The 2.30 together with the Z.50 are of 
advanced design using silicon epitaxial 
planar transistors to achieve unsur- 
passed standards of performance, Total 
harmonic distortion is an incredibly 
low 0>2% at full output and all lower 
outputs. Whether you use the Z.30 or 
Z.50 power amplifiers in your Project 60 
system will depend on personal pre- 
ference, but they are the same physical 
size and may be used with other units 
in the Project 60 range equally well. For 
operating from mains, for the Z.30 use 
PZ.5 for most domestic requirements, 
or PZ.6 if you have very low efficiency 
loudspeakers. For Z.50, use the PZ.8 
described below. 

SPECIFICATIONS (Z.50 units are 
interchangeable with Z.30s in all 
applications.) 

Power Outputs 

Z.30 15 watts R.M.S. into 8 ohms, using 
35V: 20 watts R.M.S. into 3 ohms using 
30 volts. 

Z.50 40 watts R.M.S. into 3 ohms from 
40V: 30 watts R.M.S. into 8 ohms, using 
50 volts. 



Frequency response 30 to 300,000 Hz 
_:1dB 

Distortion 0-02% into 8 ohms 

Signal to noise ratio better than 70dB 
unweighted 

Input sensitivity 25QmV into 100 
Kohms. For speakers from 3 to 15 
ohms impedance. Size 3i x 2i « i ins. 



ZZA Bu//t, tested end QA /C 

■ wU guaranteed 09/D 

ZCn Built, tested on d <f (%*% /£ 

• UU guaranteed I 119/0 



STEREO 60 Preamp/Control Unit 



Designed for the Project 60 range but 
suitable for use with any high quality power 
amplifier, Silicon epitaxial planar tran- 
sistors are used throughout, achieving a 
really high signal-to-noise ratio and excellent 
tracking between channels. Input selection 
is by means of push buttons and accurate 
equalisation is provided for at! the usual 
inputs. 

• Input sensitivities — Mag. p.u. — 3mV: 
correct to R.l.A.A. curve — IdB: 20 to 
25,000 Hz. Radio, Ceramic p.u. and Aux. 
—each up to 3mV. 

• Output -2S0mV. 



Signal-to-noise ratio— better than 70dB. 
Channel matching — within IdB. 
lone controls— TREBLE -IS to 
— ISdB at 10kHz: Bass | IS to -ISdB 
at lOOHz. 

Front panel — brushed aluminium with 
black knobs and controls. 
Size f&i>: l±x4 ins. 



Built, tested and 
guaranteed 



£9.19.6 



ACTIVE FILTER UNIT 



For use between Stereo 60 unit and two 
Z.30s or Z.50s, the A.F.U. matches the 
Stereo 60 in styling and is as easily mounted. 
It is unique in that the cut-off frequencies 
are continuously variable, and as attenuation 
in the rejected band is rapid (l2dB/octave), 
there is less loss of the wanted signal than 
has previously been possible. Amplitude and 
phase distortion are negligible. The Sinclair 
A.F.U. is suitable also for use with any other 
amplifier system. 



Two stages of filtering are incorporated — 
rumble (high pass) and scratch (low pass). 
H.F cut-off <-3dB) variable from 2BkHz to 
5kHz. L.F, cut-off (-3dB) variable from 
25Hz to 100Hz. Filter slope, both sections 
l2dB per octave, Distortion at I kHz 
(35V supply) 0-02% at rated output. 



Built, tested i 
guaranteed 



£5.19.6 



POWER SUPPLY UNITS 

Designed specially for use with the Project 60 system of your choice. 

Illustration shows PZ.5 power supply unit to left and PZ.8 (for use with Z.SOs) to the right. 

Use PZ.5 for normal Z.30 assemblies and PZ.6 where a stabilised supply is essential. 

PZ.5 30 volu unstabilised £4.19.6 PZ-8 45 volts stabilised (less mains transformers) £5.19.6 

PZ-6 35 volts stabilised £7.19.6 PZ-B mains transformer £5.19.6 



I To: SINCLAIR RADIONICS LTD., 22 NEWMARKET RD., CAMBRIDGE 



Please send 



[ for which I enclose cashlcheque 
money order 



NAME 

ADDRESS. 



|_J_ ' mSSJ 



Practical Electronics October 1970 



759 



NEW! HANDY! TIDY! 

multi-drawer 

l-N-T-E-R-L-O-C-K-l-N-G 

storage 
units 



A PLACE 

FOR 

EVERYTHING 

EVERYTHIHG 
IN ITS 
PUCE! 



c 




WW 




Newest, neatest system ever devised for scoring 
small parts and components: resistors, capaci- 
tors, diodes, transistors, etc. Rigid plastic units. 
interlock together in vertical and horizontal 
combinations* Transparent plastic drawers have 
label slots removable space dividers. Build up 
any siic cabinet for wall, bench or table cop. 

BUY AT TRADE PRICES! 

SINGLE UNITS <5ins 2±ins liins) 
Usually 36 each, OUR PRICE: 24- DOZEN 
DOUBLE UNITS (Sins :41ins liins) 
Usually 4/6 each, OUR PRICE: 40,'- DOZEN 

PLUS QUANTITY DISCOUNTS! 

Order £5 and over DEDUCT I - in the £ 
Orders £10 and over DEDUCT l'6 in the L 
Orders £20 and over DEDUCT 2 - in the £ 

PACKING POSTAGE CARRIAGE: Add 6- to 
all orders under £3. Orders £3 and over, 

packing postage carriage free. 
QUOTATIONS FOR LARGER QUANTITIES 



BD 



(Dept. PE10) 31 ALBERT RO. 
HENDON, LONDON, NW4 



DIMMASWITCH 




This is an attractive dimmer unit which 
fiti in place of the normal modern light 
twitch. The ivory mounting plate 
matches modern fittings and the control 
knob is in bright chrome. An ON. OFF 
»witch is incorporated to control 40-600 
watts of all lights except fluorescent* at 
mains voltages from 200-250V, 50 Hx. 
Competitive products sell at £4 19* 6d — 
our price is £3 4s. We also offer at 
£2 14s a complete hit of parts with in- 
structions enabling you to build this 
dimmer yourself. 

The circuit uses a miniature RCA triae 
and a diac triggering device to give 
complete reliability. Radio interference 
suppression is included. 

Post and Packing I 6d extra. 
Please send Cash with Order to: 

DEXTER & COMPANY 

ULVER HOUSE, 19 KING STREET 

CHESTER CHI 2AH 

Tel.: Chester 25883 

As supplied to H,M. Govt. DeOortments, 
Hospitols, Local Authorities, etc. 




MAKING & REPAIRING 
TRANSISTOR RADIOS 

byW. G . Oliver (G.3XT)(Publ:shed 
by Fo uf shorn Technical) (Oct.) IN- 



SECURITY ELECTRO NJCS 

by John "E. Cunningham (Oct.) 

34 



101 QUESTIONS AND 

ANSWERS ABOUT TRAN- 
SISTOR CIRCUITS 

by Leo G. Sands (Oct.) 26. 



HI-FI STEREO SERVICING 
GUIDE 

by Robert G. Middleton (Nov.) 
35 



101 EASY HAM RADIO 
PROJECTS 

by Robert M. Brown and Tom 

Kneitet (Nov.) »/- 



FOULSHAM-SAMS 
TECHNICAL BOOKS 

CW. FOULSHAM & CO. LTD.) 

YEOVIL RO., SLOUGH, BUCKS. ENGLAND 



We make computers. 
We also train computer engineers, 

Could we train you? 






We're the Education Division of one 
of the world's largest Computer manu- 
facturers (and who's better qualified to 
teach Computer Engineering than a 
Computer manufacturer?) 

Already, we've set up 39 Centres 
throughout the world to train Computer 
personnel. Now, the 40th has opened in 
London, with complete courses for 
Computer Engineers. 

The curriculum includes Basic Elec- 
tronics, Computer Circuitry, Develop- 
ment in Computer Design with the 
emphasis on practical work on the 
world's most advanced computers. 

The first courses start in September 
and last approximately 6 months. We 
are now interviewing possible students 

760 



for these courses. 

If you are interested in the challenge 
of being responsible for the mainten- 
ance of a computer installation or if you 
feel you'd like a move into today's 
fastest growing space-age industry 
we'd like to hear from you. We'll give 
you all the details, assess your abilities 
and give you an honest answer about 
future prospects. 



CONTROL DATA 



CONTROL DAT* INSTITUTE 

The Education Division of one of the 
world's largest computer manufacturers 



If there's a phone handy, ring us now at 

01-637 2171 

between 9 am and 9 pm (Mon-Fri) andaskforlMr.Jon.es. 



It's quicker and easier to phone, but if you prefer, | 
send this coupon to : Control Data Institute, 
Wells House, 77-79 Wells Street, London W1 . 
Please give me further information 

fvame (Blocn Capitals) 

Address 



I 



Age 



Phone 



Practical Electronics October 1970 



The 'KIT IDEA' by 

HEATH KIT 

Kit building is so easy the 
Heathkit way 

TRY IT FOR YOURSELF 

START WITH A SMALL 
BUT VERY USEFUL KIT 

THE NEW HEATHKIT 
BATTERY CHARGER 

PRICE ONLY 

£2«I8«0 plus 6/- Carr. 

• POWERFUL OUTPUT— UP TO 4 AMPS • FULLY FUSED 

• SOLID KNOCKABOUT CASE • SAFE DOUBLE WOUND TRANS- 
FORMER • FOR 6V OR 12V CARS • ROBUST AMMETER 

Here's the easy to build, inexpensive kit to introduce you to kit building. As well 

as the fun and fascination of building it yourself you get do-it-yourself savings. 

The clear, simple, fully illustrated instructions make assembly fool proof. This 

is the battery charger to keep your car battery in top working condition. 

Hurry, and make sure of your order today. P.S. ^-This also makes an 

excellent seasonal present. 




A Schlumbeeger Company 



™ HEATH (Gloucester) LTD., GLOUCESTER 



GL2 6EE 



Please send me a battery charger Name 
kit for which I enclose £3.4.0 Address 

including carriage. 

Post Code 



[BLOCK CAPITALS PLEASE) 



25/10A 






Practical Electronics October 1970 



76L 






TV 



RADIO & TV COMPONENTS (Acton) Ltd. 

21d High Street, Acton, London, W.3 

Also at 323 Edgware Road, London, W.2 
ALL ORDERS BY POST TO OUR ACTON BRANCH 

Terms C.W.O. All enquiries S.A.E. 



Stereo 



VS/ITH 

Viscoui 

F.ET. 

liuC 



This superb stereo system is a real price breakthrougf 

amplifier on which full details are given below, the fan._„ ... 

veneer base and transparent cover) with diamond cartridge or 2025 T( 
DUO type 2 speakers. 

Measuring l74io I0|in 6£ in, the Duo type 2 speakers are beautifully finished in teak veneer 
with matching vynair grills. They incorporate a lO^in ; 6±in drive unit and high frequency speaker, 
both of which are of 3 ohms, impedance. The Dua speaker system is also available separately at 

£6.6.0 each plus IS/- P. & P. 

Complete stereo system £41 plus £2.10.0 P. & P. 

or with Viscount Mk. II Amplifier and Magnetic Cartridge £45 plus £2. 10.0 P. & P. 




^Jhe i^la 



le \^lcL5dtc 

Teak finished case 

£9.10 

Plus P. 4 P. 7/6 
SPECIFICATION: 

Sensitivities for 10 watt output 
at I KHz into 3 ohms, Tape Head: 3mV (at 31 
i.p.s.)Mag. P.U.:2mV. Cer.P.U. : 80nW. Tuner: lOOmV, 
Aux. IQQmV. Tape/ftee. Output. Equalisation for each 
input is correct to within + 2dB (R.I. A. A.) from -20Hz to 2QKHz. 
Tone Control Ronge: Boss: 13dB at 60Hz, Treble- = !4dB at lSKHz. Toto) Dis- 
tortion; (for 10 watt output) < I -S%. Signal Noise: < — 60dB, A.C. Mains 
200-2SOV. Size I2±in long, 4iin deep, 2*in high. Built and tested. 



THE RELIANT Mk. II 

SOLID STATE 
GENERAL PURPOSE AMPLIFIER 

£7.5.0 Plus P. & P. 7 6 

In teak finished case 

SPECIFICATION: Output: 10 

watts into a 3 ohms speaker. 

Inputs: (I j for mike (lOmV). Input (2) for 

gram, radio (2S0mV) individual bass and treble control. 

Transistors.- 4 silicon and three germanium. Mains input; 220/250 

volts. Size: lOi - *i -■ 2i>n. Mk. I £6.10.0 plus 7/6 P. & P. Less teak finished 

case, __^ 





ELEGANT SEVEN Mk. Ill (350mW Output) 

7-ti-anjijtor fully tunable M.W.-L.W. Superhet 

portable. Set of parts. Complete with all components, 
including ready etched and drilled printed circuit board 
—back printed for foolproof construction. MAINS 
POWER PACK KIT: 9/6 extra, 

£5.5.0 Plus P. & P. 7/6. Circuit 2,6. Free with parts. 



THE DORSET (600mW Output 

7-tran»iator fully tunable M.W.-L.W. Superb 
portable with baby alarm facility. Setofparts. T 
latest modulated and pre-alignment techniques makes 
this simple to build. Sites: 12:8 3in. 
MAINS POWER PACK KIT: 9/6 extra, 

£5.5.0 Plus P. & P. 7,6. Circuit 2/6, Free with parts. 




Jhe Uhcount F.E.T. Mk. I £14.5.0 pius7 6p.&p. 

High fidelity transistor stereo amplifier employing field effect transistors. With 
this feature and accompanying guaranteed specifications below, the Viscount 
r-.E.T. vastly surpasses amplifiers costing far more. 

SPECIFICATION 

Output per channel—) 0W rmt. Controls — 6 position selector switch 

Frequency bandwidth 20Hz to 20kHz (3 pos. stereo and 3 pos. mono), 

± IdB " I W. separate vol. controls (or left and 

Total distortion >• I kHz h 9W 0S%. right channels. Bass -l4dB 

Input sensitivities— CER. P.U. lOOmV « 60Hz; Treble (with D.P.S. 

into 3 MCI: Tuner lOOmV into oWoff) ±!2dB « lOkHi. 

lOOKn; Tape lOOmV into lOOktl. Tape recording output sockets on 

Overload Factor — Better than 26dB. each channel. 

Signal to noise ratio- 70dB on all Size 12iin K 6in >. 2Jin in teak- 

inputs (with vol. max). finished case. Built and tested. 

Mk. II (MAG. P.U.) £15.15.0 Post & packing lO, 1 - extra. 
Specification same as Mk. I, but with Spec, en Mag. P.U. 3mV ( I kHz input 

the following inputs: Mag. P.U. impedance 47kn. Fully equalised to 

CER. P.U. Tuner. within ± IdB RIAA. Signal to noise 

ratio— 65dB (vol. max.). 




50 WATT AMPLIFIER A.C. Mains 200-250 V 

An extremely reliable general purpose 
valve amplifier. Its rugged construction 
yet space age styling and design makes 
it by far the best value for money. 
TECHNICAL SPECIFICATIONS 
3 electronically mixed channels, with 2 
inputs per channel, enables the useof 6 
separate instruments at the same time. 
The volume controls for each channel 
are located directly above the corres- 
ponding input sockets. Senaitivitiei 
and Input Impedances. Channels I 
and 2 4mV at 470K. These 2 channels 
(4 inputs) are suitable for microphone 
or guitars. Channels 1 and 4 300mV 
at Im. Suitable for most high output 
instruments Igram, tuner, organ, etc.). Input sensitivity relative to 10W output. 
Tone Controls are common to all inputs. Ban Boon + l2dB at 60 Hz/s. Ban Cut 
-13dB at 60 Hz/s. Treble Booit i- I IdB at IS KHz/s. Treble Cut -l2dB at 
ISKHz/s. With bass and treble controls central — 3d8 points are 30Hz/s and 20 
KHz/s. Power output. For speech and music 50 watts rms. 100 watts peak, 
For sustained music 45 watts rms. 90 watts peak. For sine wave 38-S watts rms. 
Nearly 80 watts peak. Total distortion at rated output 3 2% at IK Hz/s. Total 
distortion at 20 watts 015% at IK Hz/s. Negative feed back 20dB at IKHz/s. 
Signal to noise ratio 60dB. Mains voltages. Adjustable from 200-250 V, 
A.C. 50-60Hz/j. A protective fuse is located at the rear of unit. Output imped- 
ance 3. B and \ 5 ohms. __ 



Price £28.10.0 

Plus 20-'- P. & P. 



762 



Practical Electronics October 1970 




Beautifully designed to blend with the interiors of 
all cars. Permeability tuning and long wave loading 
coils ensures excellent tracking, sensitivity and 
selectivity on both wave bands, R.F. sensitivity at 
I MHz is better than 8 micro volts. Power output 
into 3 ohm speaker is 3 watts. Pre-aligned I.F. 



module and tuner together with compre- 
hensive instructions guarantees success 
first time. 12 volts negative or positive 
earth. Size 7* x 2" x 4±" deep. 



Originally sold complete for £15.4.6 



SET OF PARTS 



£6.6.0 



plus 7 6 P. & P. 



Circuit diagram 2/*, free with parti 

Speaker, baffle and fixing kit 25/- extra plus 4/- P. & P. 

Pottage free when ordered with parti 



RADIO & TV COMPONENTS (ACTON) LTD. 

Post orders to:— lid High Street, Acton, London, W.3 
Also at 323 Edgware Road, London, W.2 

Good, not despatched outiide U.K. T.rmi C.W.O. All Enquirie, S.A.E. 



R TV 



DAYS 



The New PlCtUPe-B00k wayofle^rning 

DACir ELECTRICITY (5 vols) 
»#*WlV* ELECTRON ICS(6vols) 




^ 



You'll find it easy to learn with this out- 
standingly successful NEW PICTORIAL 
METHOD — the essential facts are explained 
in the simplest language, one at a time, and 
each is illustrated by an accurate, cartoon- 
type drawing. The books are based on 



the latest research into simplified learning 
techniques. This has proved that the 
PICTORIAL APPROACH to learning is the 
quickest and soundest way of gaining mastery 
over these subjects. 

TO TRY IT, IS TO PROVE IT 



The series will be of 
exceptional value in 
training mechanics and 
technicians in Elec- 
tricity, Radio and 
Electronic*. 

WHAT READERS SAY 

" / kave looked at each book and must confess they are very good, 
everything is made so simple, which makes reading a pleasure," 

R.H.H.G-.BIandford. 

" ' I find the information contained very aptly illustrated and composed" 

D.G., Twickenham. 

" I would like you to know once again that I have read parts of each 
volume and think they are excellent reading material. Easy to under- 
stand, easy to read and the subjects are not flooded with reams of 
unnecessary calculations which most electrical books delight in." I 

P.B.. New Maiden. ' 

A TECH-PRESS PUBLICATION 



POST NOW FOR m/S OFFER.'! 






Practical Electronics October 1970 



To The 5ELRAY BOOK CO., 60 HAYES HILL, HAYES, BROMLEY, KENT BR2 7HP 
Please send me WITHOUT OBLIGATION TO PURCHASE, one of the 
above sets on 7 DAYS FREE TRIAL, I will either return set, carriage paid, 
in good condition within 7 days or send the following amounts BASIC 
ELECTRICITY 75,'-. Cash Price or Down Payment of20<- followed by 3 
fortnighdy payments of 20- each BASIC ELECTRONICS 90/-. Cash 
Price or Down Payment of 20/- followed by 4 fortnighdy payments of 20/- 
each. This offer applies to UNITED KINGDOM ONLY. Overseas 
customers cash with order, prices as above. 

Tick Set required (Only one set allowed on free trial) 

BASIC ELECTRICITY BASIC ELECTRONICS 

Prices include Postage and Packing. 

Signature 

(// under 1 8 signature required of parent or guardian) 

NAME , 

BLOCK LETTERS 

FULL POSTAL 

ADDRESS 

763 




INTERNATIONAL 



AUDI 




OCTOBER 20-24 

Hear and compare the world's finest sound repro- 
ducing equipment for the home. The top loudspeakers, 
amplifiers, tape recorders, pick-ups, tapes, and 
accessories have been brought together under one 
roof to give you a superb Festival of Sound. 
Famous manufacturers from all over the world will be 
demonstrating their products in specially constructed 
studios which will enable you to hear the Sound at its 
best, 

Each day a programme of special live presenta- 
tions and lectures will be held in the Hi-Fi 
Theatre . . . and there will be two cinemas 
continuously showing films of instruction and 
interest. Entrance to both theatre and cinemas 
is FREE. 

Everyone who takes pleasure in using and listening 
to Hi-Fi equipment of the highest standard must 
visit this International Audio Fair. 

ADMISSION 5 - 

0LYMPI1 

10am-9pm LONDON W14 

EXCLUSIVE SHOWING TO THE TRADE BY 
INVITATION ONLY MONDAY 19 OCT. 2-9 pm 

Apply for your ticket to the organizers: 

Audio Music Fair Sales Office, lliffe Exhibitions Ltd., 

Dorset House, Stamford Street, London SE1 

Telephone: 01-928 3333 Ext. 223 



YATES ELECTRONICS 

(FLITWICK) LTD. 

RESISTORS 

High stability carbon film. Very tow noise. 05W 5% 4-7n 
to 2-2 Ma 2 5d each, 1 00- 2d each, 0-5W 10% 4-7li to 
10MO 2d each, I00- I75d each. Quantity price applies for 
any selection. Ignore fractions on total order. 

DEVELOPMENT PACK 

0-5 watt 5% resistors 5 off each value 4-7Q to I MQ 
325 resistors EI2 series SO/-. 
650 resistors E24 series I00/-. 

4 WATT WIRE WOUND RESISTORS 1/6 each. 

10% 10, 18, 2-7, 3-3, 39. 4-7, 5 6, 6-8, 8-2 ohms. 
5% 10, 15, 20, 25, 39, 50, 100, 200 ohms. 
MULLARD POLYESTER CAPACITORS ^10% 

400V: 0-00 1 /(F, 0-00I5/-F, 0-0022/<F, 0-Q033.«F, 0-0047/<F, 6d. 

0-0068/tF, 001 /<F, OOIS/'F, Q022.»F, 0-033/-F, 7d. 0-047 /<F, 9d. 

0-06B//F. 0-l/«F, lOd. 

160V: 0-01 »F, 0-015»F, Q022.»F, 0033/<F ; 0-047/.F, 0-068/iF, 7d. 

0I/-F, 9d. 0-I5/.F, 022/-F, lOd. 0-33/*F, 1/3. 0-47,-F, 1/6. 

068,-F, 2/3. 1-0^,2/6. 

250V: P.C. mounting miniature ..20%: 01 /<F, 0-015/fF, 

0-022/^F, 7d. 0-033/.F, 0047//F, 0068,«F, 8d. 0l/<F, 9d. 

OIS^F. 0-22,»F, I/-. 0-33/-F, 1/4. 

MYLAR FILM CAPACITORS 

100V: 0-00 1 /<F, 0002/(F, 0005/'F, 0-OI/iF. 002/<F, 6d. 0-05/iF, 

0l/(F, 8d. 0-2/iF, I/-. 

CAPACITOR DEVELOPMENT PACK 

Selection of ceramic and polyester capacitors lOOpF to I0/<F. 

Total 100 capacitors, £2.18.0. 

MINIATURE ELECTROLYTIC CAPACITORS 

(-10% ^S0%) 



JOOpF 
200aF 
120^-F 



I6ijF 10V 


IOuF 


12V 


40 M F 


16V 


64uF 10V 


ISpF 


12V 


64jtF 


25 V 


125|uF I0V- 


SOfif 


12V 


25nF 


25V 


200,uF 10V 


100/iF 


12V 


8^F 


40V 



16/iF 
50«F 
2-5/iF 
I O/.-F 



40V 
40V 
64V 
64V 



I /- each 

250/* F 12V, I00/<F 40V 1/6. 1000/.F 25 volt 6/-. 2500/<F 
25 V 9/-. 500/1 F 50 volts 5/-. I000/'F 50 volt 8/-. 

CERAMIC DISC CAPACITORS 

lOOpF, ISOpF, 220pF, 270pF, 330pF, 470pF, 560pF, 680pF, 

lOOOpF, 2000pF, 5000pF, lO.OOOpF, 5d each, 

0-02,"F 800 volt fid each, 

GANGED STEREO POTENTIOMETERS 

i watt carbon track Skil SkCl to I MCI -'- I Mfl log or linear 

8/- each. 

SKELETON PRE-SET POTENTIOMETERS 

Linear: 100, 250, 500 ohms and decades to 5M ohm 20% 

j£250k£i, :..:30%, 250k O. Horizontal or vertical P.C. 

mounting (0-1 matrix). 

Miniature 0-3 watt 1/- each. 

Sub-miniature 0-1 watt lOd each. 



TRANSISTORS 



AC 126 41- 
ACI27 41- 
ACI28 41- 
ADI40 8/- 
AFII5 3/6 



AFH7 3/6 
BC107 3/- 
BCI08 2/9 

BCI09 3/- 
BFY5Q 4/6 



BFY5I 
BFYS2 

BSY56 
BSX2I 



3/9 
4/6 

6/- 
5/- 



DIODES— OA85, OA9I, I- 

ZENER DIODE 

400mW 5% 3-3V to 33V 3/6 

SILICON RECTIFIERS 

IN4006 800V I A 4/- 
IN4007 1000V I A 4/3 

VEROBOARD 



2N2926 2/6 
each 



2N3055 14/6 
2N3703 3/3 

2N3705 " 

2N37II 

ORPI2 



3/6 
3/3 

9/6 



BYZ10 600V I0A 
BY236 800V 0-8A 



015 0- 

Macrix 



2*x 
2±X 
3fx 
3| x 
17 X 
I7x 
17 x 



3* 

5 

H 

5 

3! 

5 (plain) 



3/3 


3/9 


41- 


4/6 


41 


4/6 


5/3 


5/3 


IS 


— 


11/6 




15/- 


— 



I7x3i (plain) 
17 ;<2i (plain) 
2£x5 (plain) 
2jx3J (plain) 
Pin insertion too! 
Spot face cutter 
Pkt. 36 pins 



0-15 

Matrix 
10/6 

7/6 

3/6 

3/- 

m 

7/4 
3/- 



0-i 



9/4 
7/6 
J/- 



ROTARY SWITCHES 

IPI2W, 2P6W, 3P4W, 4P3W, 4/6. 

GRADUATED DIALS 

For use with potentiometers, selector switches, etc., 3/3. 

C.W.O. please. 1/6 po« *f"f packing on ordtn under CI. 
Export Enquiries welcome] 

ELST0W STORAGE DEPOT, KEMPSTON HARDWKK, BEDFORD 



764 



Practical Electronics October 1970 



AAY30 
AAZI3 
AC 1 07 

AC 126 
AC 1 27 
ACI27Z 

AC 1 26 

AC 1 76 

ACIB7 

AC IBS 

ACYI7 

ACYIB 

ACYI9 

ACY20 

ACY2I 

ACY22 

ACY27 

ACY28 

ACY29 

ADHD 

AD I -49 

AQI6I 

ADI62 

AOTMO 

ADZ It 

AD2I2 

AFI02 

AFI06 

AFI 14 

AFH5 

AFI16 

AFII7 

AFI 16 

AFI 21 

AFI24 

AFI2S 

AFI 26 

AFI 27 

AFI 39 

AFI 78 

AF 1 79 

AFI SO 

AFI66W 

AFIB6C 

AF239 

AFZI I 

ASY26 

ASY27 

ASY2B 

ASY29 

ASZ2I 

AUYIO 

B2M 

B3M 

BAI02 



1/7 BAIII 
1/1 BAM 4 
7/7 BAXI3 
5/- BCH3 
4/- BCII5 
9/6 BCII8 
4/ BC 1 2S 
Sl~ BCI26 
6/- BCI43 
•/- BCI45 
5/9 BCI47 
4/- BCUB 
4/- BCI49 
3/10 BCI69 
3/10 BC17I 
3/9 BCI82L 
1/6 8CI83L 
1/8 BCI84I. 
7/6 6C2I2L 
11/- BCYIO 
11/6 BCYI2 
7/6 BCY30 
7/6 BCY3I 
12/6 BCY32 
32/- BCY33 
39/- BCY34 
12/6 BCY38 
tm BCY39 
5/- BCY70 
§/- BCY7I 
5/- BCY72 
5/- BCZI I 
S/IO BDI2I 
6/- BDI23 
5/- BDI24 
4/2 BDY20 
3/6 BFI63 
3/6 BFI67 
13/- BFI73 
9/6 BFI78 
11/6 BFI79 
12/6 BFIBO 
8/- BFI8I 
fl/- BFIB4 
776 BFI85 
Si- BFI94 
4/5 BFI95 
6/- BF200 
4/5 BFXI3 
6/- BFX29 
7/6 BFX44 
30/- BFX84 
12/6 8FX8S 
15/- BFX88 
9/- BFYSO 



6/- 8FYSI 
1 BFY52 

1/6 EFY53 

3/- BFY90 

6/6 BSXI9 

7/6 BSX20 
11/- BSX2I 
11/- BSX76 
15/- BSY27 
15/- BSY29 

2,9 BSY95 

3/3 BSY95A 111 

3/- BYZI4 33/3 

1/9 BYZIS 

2/- C 1 1 1 

1/3 CI I IE 
1/10 C426 

3/- CRI-05IC •/ 

3/4 CRI-401CI0,- 
10/- DI3TI 10'- 
12/- GET 1 6 12(6 

S/- GET 1 02 6' ■ 

5/6 GET 1 03 5/- 
10/- GETIII 5/- 

4/- GETII3 

5/- MJ480 

6/- MJ46I 

9/6 MJ490 
3/10 MI49I 

7/B MPFIOI 

3/1 MPFI03 
7/6 MPFI04 
22/- MPFI05 
22/- NKTI I 
20/8 NKTI 2 
10/8 NKT32 
9/- NKT42 
5/- NKT43 
6/~ NKT72 
10/6 NKT73 
I1'6 NKTIOI 
7 6 NKTIOI 
7/6 NKTI 03 
17- NKTI04 
3/- NKTI OS 
3 6 NKTI 06 
1,'- NKTI 07 
10/6 NKTI OB 
5.'- NKTI 09 
6/2 NKTI21 
I - NKTI 22 10/ 
5,1 NKTI 23 9/6 
6/9 NKT124 6/5 
3/1 NKTI2S 4/6 
476 NKTI 26 41- 



33 3 
18- 

12 - 
• 1 



20 6 
27 - 
22 6 
296 
1/6 
7/6 
7/6 
B/- 
7/6 
5/3 
6/- 
•/- 
6l- 
3/9 
1/7 
61- 
*/- 
6/- 
61- 
6/- 
6/- 
6/- 
«/- 
6/- 
10/6 



NKTI27 

NKTI28 

NKTI29 

NKTI35 

NKTI37 

NKTI4I 

NKTI42 

NKTI43 

NKTI44 

NKTI5I 

NKT1S3 

NKTI 54 

NKTI6I 

NKTI62 

NKTI63 

NKTI 64 

NKTI6S 

NKT20I 

NKT202 

NKT204 

NKT205 

NKT206 

NKT208 

NKT2I0 

NKT2II 

NKT2I2 

NKT213 

NKT2I4 

NKT215 

NKT2I6 

NKT2I7 

NKT2IB 

NKT2I9 

NKT22t 

NKT222 

NKT223 

NKT224 

NKT225 

NKT226 

NKT227 

NKT228 

NKT229 

NKT23I 

NKT232 

NKT237 

NKT238 

NKT239 

NKT240 

NKT24I 

NKT242 

NKT243 

NKT244 

NKT24S 

NKT26I 

NKT262 



10/6 NKT263 4/8 NKTI2429 OC205 9/- 40316 

10/- NKT264 4/J 10 6 OC206 15/- 40317 

8/6 NKT265 5/6 NKTI 1329 OC207 13/- 40319 

6/1 NKT270 6/- 3/11 OCP7I 18(6 40320 

6/1 NKT27I 2/10 NKTI 3429 ORPI2 10/- 40323 

10/6 NKT272 2/10 1/1 1 ORP60 ■/- 40324 

10/- NKT273 1/8 NKTI 6229 ORP6I 8/- 40326 

9/6 NKT274 2/10 8/5 ORP63 9/- 40329 

*l~ NKT275 1/4 NKT20329 P346A 1/9 40344 

6/- NKT276 3/6 6/8 RAS3I0AF6/- 40347 

6/ NKT279A2/6 NKT20339 RAS50BAF 40148 



«/- NKT28I 
61- NKT30I 



3/- 6/4 

IB/- NKT3S2I9 SIM 



6/- NKT302 IKS 15/9 S4M 

6/- NKT303 17/8 OCI9 5/- ST2 

6/8 NKT304 9/10 OC20 19/6 T1407 

«/- NKT35I 10/- OC22 8/- TIC4S 

6/- NKT352 17/6 OC23 10/- TIS34 

6/- NKT36I 10/- OC24 10/- TIS44 

6/- NKT362 20/- OC25 7/6 TIP3IA 

6/~ NKT40I 14/6 OC26 

6/- NKT402 IS/- OC28 

6/- NKT403 14/9 OC29 

4/1 NKT404 11/- OC35 

J/» NKT405 II.'- OC36 

3/9 NKT406 9/11 OC4I 

4/7 NKT42028/II OC42 

3/5 NKT45I 9/11 OC43 

3/7 NKT452 9/6 OC44 

7/6 NKT453 6/6 OC45 

91- NKT603F 4/8 OC70 

6/- NKT6I3F 5/2 OC7I 

4/7 NKT6S4F 4/2 OC72 

7/- NKT67S 6/8 OC74 

6/- NKT676 5/- 0C7S 

5/- NKT677F OC76 

2/7 3(10 OC77 

3/6 NKT703 8,'- OCBI 
11/- NKT7I3 3/10 OC8ID 

9/6 NKT7I7 S/tO OC8IZ 

6/6 NKT734 4/11 OCB2 
1/1 I NKT736 6/2 OC82D 

6/- NKT773 3/7 OCB3 

6/- NKT774 6/- OC84 

5/9 NKT00I3 6 '6 OCI23 

4/- NKTI04I9 OCI39 

4/- 3/10 OCI40 

3/10 NKTI0SI9 OCI41 

3/9 4/5 OC170 

2/11 NKTI0339 OCI7I 61- 40309 
12'- 4/7 OC200 7/6 403 10 

1/1 NKTI 0439 OC20I M 40311 
3/- S/5 OC202 11/6 40312 

4/1 NKTI2329 OC203 7/6 40314 
4/3 B/5 OC204 8/_ 40315 



40360 

19/- 40361 

13/6 40362 

9/9 40370 

9/8 404O6 

Ml- 40408 

17/6 40462 

1/9 40467 

12/4 4046BA 

6/6 TIP32A 14/10 40602 



9/1 2N7 1 I A 
7/3 2N743 

10.9 2N744 
7/] 2N9II 
6/6 2N9I4 
9/1 2N9I8 
7/3 2N929 
4/9 2N930 
5/3 2NII3I 
7/6 2NII12 

10/3 2NI302 
8/6 2NI303 



7/6 2N3709 
4/6 2N37I0 
41- 2N37II 
10/- 2N38I9 
3/11 2N3820 
1/5 2N3B26 
5/2 2N3866 
61- 2N4037 
6/- 2N4058 
6/- 2N4059 
1/7 2N4060 
4/6 2N406I 



9/6 2NI304 4/11 2N4062 
lt/6 2N1305 4/11 2N4284 
6/~ 2NI206 6/- 2N4287 



12/- V205 
13/- V405A 
10/- ZTXI07 
12/6 ZTX108 
5/- ZTXI09 
4/6 ZTX300 
4/6 ZTX30I 
J/- ZTX302 
3/- ZTX303 
2/6 ZTX104 
3/- ZTX3I0 
4/6 ZTX3II 
•/- ZTX312 
4/6 ZTX3I3 
5/- ZTX3I4 
3/- ZTX320 



10/- IB0BT1C 

9 3 IN34A 

2/7 IN60 

2 2 IN64 

2/7 IN82A 

2/7 IN87A 

2/8 INI9I 

3/8 IN9I4 

3/8 IN37I3 

5/5 IN37I7 

I '7 IN4I48 

1'- IS44 

l'l IS 100 

2/1 ISI07 

2/1 IS4I0 

6 1 IS4I0R 



11/3 2NI307 

10/1 2NI308 

11/3 2NI309 

16/6 2NI6I3 

7/- 2N17II 

8/- 2N2I47 

10/- 2N2I48 

41- 2N2I60 

41- 2N2369 



6/- 2N4288 
6/- 2N42B9 
6/1 2 N 4290 
4/6 2N429I 
5/- 2N4292 
16/3 2N4B7I 
12/6 2NSI72 
12/6 2N5I74 
3/4 2N5I7S 



4/- 2N2369A1/II 2NSI76 
9.-6 2N26I3 7/6 2S001 
4/6 2N26I4 4/- 2S002 
3/- 2 N 2646 10/- 2S0O3 
3/6 2N2904 8/10 2S004 
30/- 2N2904A 9/9 2SO0S 
30/- 2N2905 12/11 2S006 
1/6 2N2905AI3/1 2S0I7 
0/0 2N2906 8/10 2S0IB 
1/2 2N2906A 2S0I9 

6/8 10/10 2S020 

5/1 2N2923 4/- 2SI04 



4/6 ZTX32I 5/ 1 1 2G302 
4/- ZTX330 J/7 2G339A 



It/- ZTX33I 
5/- ZTX34I 
J/- ZTX342 
4/6 ZTX500 
3/- ZTX50I 
7/- 
5;. 



4/4 2G37I 
3/7 2G37IB 
4/2 2G374 
3/1 2G3BI 
1,1 2NI74 
ZTX502 1/1 1 2N385A/ 
ZTXS03 3/4 2N388A 



7/- ZTX504 7/11 2N404 
2/6 ZTXSIO 3,4 2N696 
3'- 402S0 10,9 2N697 
6/6 2N698 
9/- 2N706 
6(9 2N706A 
9/6 2N708 
7/3 2N709 
7/3 2N7M 



5/1 2N2924 

3/9 2N292S 

5/- 2N3053 

1/ 2N3054 

1/- 2N305S 

51- 2N139IA 6/ 

SI- 2N3393 5/ 
16/- 2N3394 
2N3402 
15/ 2N3403 
4/6 2N3404 
3/6 2N3S25 
3/6 2N3702 
6/- 2N3703 
2/4 2N3704 
2/6 2N3705 
3/3 2N3706 
8/6 2N3707 
7/6 2N3708 



41- 2S301 

3/6 2S302 

S/- 25303 

12/6 25304 

IS/- 25306 

2S320 

2S32I 

4/9 2S322 

5/6 2S323 

3/6 2S70I 

7/6 2S702 

21/9 2S703 

2/6 2S7II 

2/5 2S7I2 

3/2 2S720 

2/8 2S732 

3/3 2S733 

2/10 3NI2B 

l/IO 3NI40 



2/ 

1/3 

ft 
I 6.9 

6/- 
25/- 
H/- 

1/4 

| 

4/- 
4/6 
31- 

| 

31- 
3/- 
J/~ 
6/9 

II- 
10/6 

10,6 
t/- 
10/- 

11/6 
12/6 

IS/- 

if 

15/- 

17/6 

19/6 

20 

11/0 

0/4 

7/6 

10/- 

11/6 

13/- 

»/•■ 

61- 

■/- 

10/- 

■/« 

11/4 

11/6 

26/6 

34/6 

25/- 

8/6 

3/11 

13/9 

15)1 



3NF4I 

3NI42 

3NI41 

3NI52 

AAII9 

AAY1I 

AAZI2 

AAZI3 

BAI 10 

BAIII 

BAI 12 

BAI IS 

BAI 30 

BAY3I 

BAY3B 

BY 1 00 

BY 127 

BYXIO 

BYX36/I50 

1/6 
BYX 36/300 

1/10 
BYX36/600 

!/• 
BYY2I 
BYY23 
BYY2S 
BY Y 142 
BYZtO 
BYZI2 
BYZI3 
CG6E 



14/4 
10/9 
11/1 
17/3 

2/ 
2/- 
61- 
2/4 
61- 
61- 
IB/- 
1/6 
3/- 
2/6 
3/- 
41- 
41- 
31- 



CG63 

EA403 
E8383 
EC40I 
EC402 



25/- 
26/3 
31/9 

3/9 
•/- 
61- 
S/- 
4/- 
1/- 
1/* 
316 
SJ- 
4/8 



GEX45/I 4/ 



GJ6M 

OA5 

OAIO 

OA47 

OA70 

OA73 

OA79 

OABI 

OA85 

OA90 

OA9i 

OA95 

OA200 

OA202 

OA2II 

SDI9 

TD7I6 



4/- 
1/B 

st- 
ilt 

!/• 
1/8 

i/a 
i/a 
t/e 

1/8 

i/a 
i/a 

t- 

Sl- 
id, 
12/- 



^PNS^ s ,if?|2N38i9 7/-I NEWS NEWS NEWS NEWS... 

BaoR^oVi 1 ! *+ r £~m+m SILICON REQIFIERS ^^^r^^^r^L^^ 

_^^£_^_ ±J_ >W__ t^ 8H tm s.ttors Led.— AH Newmarket products row available at 

■ I Amp Miniature Moulded June- ■ .lnd«»tn»l User pricei. All R.C.A. Semi-cenduciors and 

•i uio7l .,„■ Sir A inn IFlB £ion «e«ifiers. 'n«i rated circuits now also . available from L.ST, at 

2N487 6/9B Mt l A '00 35/- ■ p ,, n ., t± „ B c „„ I IndM.tnal User pricei. Many Mullard, General Electric, 

'1 ' P././. 1-14 25 + 100 + 500+ ■ Texas types also ex stock at L.S.T. at Induitrial User 

Motorola unijunction H3IF2 l&lfk ■ 'N4O0I 50 1/6 1/4 1/2 I/- I Prices and better. Ukra resistors, Mullard Capacitors, 

25^5/9 100 J- 4/9 ■"" , * **/« ■ I N 4002 100 1/6 1/4 /l !/_ I Veroboard, Repanco coils and other misc. components 

M Infra-red devices ■ I N4003 200 2/- 1/9 16 1/3 I ""eked in targe quantities. Official Intemattonat Rectifier 

B^BjaB IN4004 400 II- 19 1/6 13 I Centre stockists. 

2N3055 I5/-10CP7I | 9 /6| IKES! S8S iiS hHBH-^.NliH.^HHKHHHH 

MSwattsiliconpower I Mullard II IN4 °° 7)W0 «" » 2/9 2/6 I INTEGRATED CIRCUITS 

25 + l3/- nS 'r00 r + II'- I Pn<"<K«n«iitor ■ | n th e event of any 1N4000 series ■ ^,„. > -. . . . 

Z_7 luv +'"< ■ 2S -<- 17,1 ion , , a- o H B ° m S temporarily out of stock we I Some R.C.A, Linear Typem 

t - mm m m m m ~- mmmmm — m m u ^^^^ m < mm ^^^m reserve the right to send higher ■ CA300S 23/6 CA3020 25/3 CA302BB 21'- CA3043 27'6 

7W^?7^ ^^■B T™ ge ty 5* s at no excra eh » r ge. ■ CA30II 14/9 CA302I 31/3 CA303S 24/6 CA3044 24'- 

IRC 20 7 - ■ New , low integrated ■ 1000+ and over prices on appli- ■ CA3012 17/9 CA3022 26/- CA3036 14 6 CA3045 24 6 

I . ■ , . c u. • ' II f,'^. uit pri «* F»irchild ■ ««'«"• I CA30I3 21/- CA3023 25 1 CA3039 6 CA3046 IS/2 

Int. Rectifier thyristor ■ (U S; A.) micrologic ■ I CA30I4 24/9 CA3026 10 * CA304I 21 9 CA3048 40/9 

(i&r CI06BI1 ■ R.T.L. epoxy case TOS ■ I CA30IBI6/9 CA3028A 14 9 CA3042 21 % CASOsF uX 

(similar cioeBl) ■ temperature range IS ■ * 

254^^IOO^fS/-^B C. to 55 C. p^B^BBlfl Application Notes for each individual 2,'6d. per copy 

■■■■"« ii! 9o'|^ P ™ + ■ ZENER DIODES I ^4 gffi A w^t ffl^ ! ' ' % 

KWItoMBta.lg^f Lrl^StUfc ,52082 82,0, ■ *£& ftlWuSSSfe*" " I 

25+ 18 100+ 16 I I 10/6 10/- 9/6 V ■ "«9 3-9 vok IS2I00I0 £lt ■ SL702C Pl«sey Li«e P ' Ht 

■^■■■■^■■H Da " »" d crrcuits ■ "043 4-3 volt IS2II0 II volt ■ TAA263 Mullard Linear . . fl 

RV |17 (T^ali V t,c { f • ?-P*i e ' at 2/6 - H li^I r'l vo c <S2I20 l2volt ■ TAAI93 Mullard General Purpose Amplifier io',- 

JuMt» ^'" M £^"1? 3 ? Suggested ■ "056 5 6 volt IS2I60 16 volt It TAA3I0 Record Playback Amplifier " 

Mullard Pl«t.c ■ Circu.ts for Micro- H |2062 6-2 vole I S2I 80 18 volt ■ TAA320 MOS LP Amplifier f? " 

HV rectifier 800 p,v. ■ log.c". at 3/-. ■ S2068 6^8 vott IS2270 27 vok ■ TADtOO Mullard IC Receiver [i',7 

I amp. (similar BY 1 00. ■ TO^j, DIL conversion ■ IS207S 7-5 volt I S2300 30 volj ■ 3NB4 GE SiMcJn CoXXed Switch V. \ \ f& 

"t./ ■■ spreaders adaptors at BIB rRlt.E5: 1-24 3/6 25-99 2/9 H| _ ***' 

3.'3 100 - 3 - | 1/6 each. M 100+ 1/3 I Dat:1 Sheets I/- (SL403A 2/6. IC 10 data not sold separately). 

S^^^»^^tSSS?i LIT. ELECTRONIC COMPONENTS LTD. 

v^^^X^^^Z SS3 ! SS :: ¥ Z ^ i% 7 C0PTF0LD ROAD 

relXr 1 ,^^^ BRENTWOOD, ESSEX 



Practical Electronics October 1970 



765 




SPECIAL OFFERSt 

liarrard 8PH5/11 IK (ml (ioidring 0800 
cartridge and wooden plinth anil plastic 
cover. Total list price £35. 
OUH PRICE 120.16.8. Cacr. 10/-. 
CiOLDRING GL69/2 lltted Goldring ti800 
cartridge complete with deluxe base and 
cover. Total list price £50.16.0. 
OUR PRICE 139. Carr. 20/-. 

* TRANSISTORISED FM TUNER * 

« TKAXS1MTO R 
HIGH QUALITY 
TUNER. SIZE 

ONLY 6 4 2Jltt. 
8 I.F. slages. 
llouble tuned dis- 
criminator. Ample 
output to feed moat 
I amplifiers. Oper- 
ates ou HY Battery, Coverage 88-108 Mc/s, 
Ready built ready for use. Fantastic value 
tor money. £6.7.6. 1*. £ P. SJfS. 
Stereo multiplex adaptors 09/6. 

BELCO AF-5A 

SOLID STATE SINE SQUARE 

WAVE C.R. OSCILLATOR 



Is-L'DO.OOOHz; 



Output max 
+ 10dB llOkll). 
Operation 
internal 
batteries. 
■ active iwo-tone ease 7|in '-< Sin 
Price 117.10. Carr. 3/S. 

CLASS D WAVEMETERS 

A crystal controlled hetero- 
dyne frequency meter 
covering ]-7rS Ho/*. 
Operation on 6 V d.e. 
Meal (or amateur use. 
Available in good used con- 
dition. 15,19,6. Carr. 7,'«, 
nr brand new with acccs- 
mto. 17.19.6. Carr. 7/6. 



B.C. 221 FREQUENCY METERS 

latent release 1 25kHz to 20Mllz. Excellent 
conditio!!. Fully tented and checked and 
complete with calibrator charts. 
127.10.0. each, Carr.. 10,'-, 





TYPE 13A 




DOUBLE BEAM 
OSCILLOSCOPES 

An excellent general pur- 
pose D/B oscilloscope. 
T.B. i! e/s-750 ke/e, 
Handwldth 5-5 Mo/s. 
SeilHltiviiy 33mV/CM. 
Operating voltage 0/110/ 
200/250 V, a.e. Supplied 
In excellent working con- 
dition. 122.10.0. 
Carriage 30/-. 




MARCONI CT44' 
TF956 AF- 
ABSORPTION 
WATTWIETER 

1 /i/watt to C wattn, 
£20. Carr. 20'-, 





HALF PRICE OFFER ! SINCLAIR STEREO 25 

Hi-Fi solid state pre-ariipllner and control unit 
incorporating treble, bass, volume and balance 
controls. Switched input tor p.u. (magnetic and 
ceramic), mike and radio. Will also accept tape 
head. Operate* ironi 9V-12V battery (20V max. 
7 5 mA >. Frequency response 2 fi Ri~30kH2 ± 1 ilB , 
Noise level better than — 50dB on all inputs, 
Principally designed tor use with Z12 Amplifier but 
full Instructions are supplied to enable i t to be used 
with any amplifier. Size «}* X 84* x 21* overall 
plus knobs. Brushed and polished aluminium front 
panel with matching knobs. Supplied brand new 
and guaranteed, with full instructions. 




alprketa.lil.H. 

90/6 V: p ' 



UNR-30 4-BAND COMMUNICATION 
RECEIVER 

Covering 550 Kc.'s 30 Mc/s. Incorporates BFO. lluilt-m 
[speaker and phone lack. Metal cabinet. Operation 220,' 
240V. a,c, Supplied brand new, guaranteed with 
Instructions. Carr. T/li ||J g ns _ 





SOLARTEON CD. 711S2 DOUBLE BEAK 
OSCILLOSCOPES. D.C. to Me;e. Perfect 
order. £05. Carr. 60/-. 

T0-2 PORTABLE OSCILLOSCOPE 

A general purpose Ion- 
cost economy oscillo- 
scope for everyday use. 
Y amp. Bandwidth 
S CPS-1 MHZ, Input 
imp. 3 roegfj 25 I'.F. 
Illuminated scale. 2ln. 
tube. US ; 180 . 
230mm. Weight 81b, 
220/2*0 V a.c. Supplied 
brand new with hand- 
book. £22.10.0. Carr. 10/-, 

TRANSISTORISED L.C.R. A.C. 
MEASURING BRIDGE 

A new portable 
bridge offering ex- 
cellent range and 
accuracy at low 
cost. Ranges: B. 
lfl-11-1 megfl 
6 Ranges -[;l/i. 

i.i »e - i i i 

HENRYS Ran- 
ges -2%. C. lOpF 
_I110mFd. 
Han ges -2%. TURNS RATIO 1:1/1000- 
1:11100. o Ranges ±1%. Bridge voltage at 
1,000 cps. Operated irom i) volts, lOO/jA. 
Meter indication. Attractive 2 tone metal 
ease. Size 7! * 5 "Sin. 120. P. & P. 6/-- 



UFAYETTE SOLID STATE HA600 RECEIVER 



5 BAHD AM.CWj'SSB AMATEUR AHD SHORT 
WAYE 150 kc's-400 to/i and 560 kc/s-30 Kc/i 
F E T front end • 2 mechanical niters • Huge 
dinl • Product detector • Variable BFO • Noise 
limiter • S meter • 21in Bindspre&d • 230V 
s.c./12V d.e. neg. earth operation • RF gain 
control. Size ISio x SI Id k 8Hn. Weight 181b. 
EXCEPTIONAL YALUE. MS. Carr. 10/-. S.A.E. 
lor full details. 
LAFAYETTE HA.BQQ 8-BASD AMATEOR RECEIVER. {57.10.0. Carr. Paid. 



TRIO COMMUNICATION 
RECEIVER MODEL 9R-59DE 

■i band receiver covering 660Kc/« to SOMe/s. 
■ -iiulliuious and electrical liandspresid on 10, IS, 20, 
40 and 80 metres. 8 valve plus 7 diode circuit. 
4/B ohm output and phone jack. 8SB-CW • ANL 
• Variable BFO • S meter • Sep. ban dsp read 
dial • IK -USKcj's • Audio output loW. • 
Variable EF and Al' gain controls. HB/250\ 
A.C. Mains. Beaut ifnl I >• design rxl. Size; 7 X 15 « 

lUin vwiu instruction t.i.tunal and service data. 142 Carriage paid. 

THIO COMMTJHICATIOH TYPE HEADPHONES Normally M.19.6. 

OUR PRICE 13.1S.0 if purchased with above receiver. 



TRIO JR-500SE 10-80 Metre 
AMATEUR BECEIVER 165 



TRIO TS 510 AMATEUR TRANSCEIVER 
with speaker and msini F.S.U. £180 




RCA COMMUNICATION 
RECEIVER AR88D 

Latest release bv ministry BRAND HBW in 
original cases. IKJ-250V a.O. operation, Irc- 
Cueucy in 8 Bands. 030Kc/s-32Mc/s continuous]. 
Output impedance 2S-000 ohms. Incorporating 
crystal filter, noise limiter, variable BFO, variable 
selectivity, et«. Price f 6S . Carr . £2 , 



LAFAYETTE PF-60 SOLID STATE VHF FM RECEIVER 

A completely new transistorised receiver covering 
152-174 Mcy's. Fully tuneable or crystal controlled 
(not supplied) for llxed frequency operation. In- 
corporates i INTEfiUATED CIRCUITS. Built 
in speaker and Hluiulnated dial. Brjuelch tvud vol- 
ume controls. Tape recorder output. 76 fl aerial 
Input. Headphone jack. Operation 230Y. A.C,.' 
12V. D.C. Neg. earth, £37,10.0. Carr. 10,'-, 

TELETON MODEL CR 10T AM/FM STEREO TUNER AMPLIFIER 

A new model from Teleton. 31 solid state 
devices. 4-J-4 watt output. Inputs for 
cerarni e/cry stal cartrid ge. Frequency range 
AM S40-1000 KHz FM 83-108 MHz. Auto- 
matic FM stereo reception. Stereo indicator. 
Controls: Tuning, (unction selector, Tone 
and R & L volume controls. AFC Bwltch. 
Stereo headphone socket. Size: 13 J" V. 3 J* 
< i * appro K, Pr i ce 128. 19. . Carr. 7/0 . 





'■"'"* mA 


■ 


| 

1 
1 



CLEAR PLASTIC PANEL METERS 

First grade quality Moving Coil panel meters. 
Type MR 381*. l s ',' 3 .ln square fronts. 



5<hiA 



500-0-500/jA £7/6 

1mA B7/S 

1-0-lniA S7/B 

2mA »7/« 

5mA B7/8 

10mA 27 6 

750mA S7/8 



'50mA ,87/8 

100mA 87/fl 

150mA 27/8 

200mA 87/8 

300mA 27/8 

SOOmA B7/8 

3V. D.C 87/8 

10V. D.C 87/8 



350V. D.C... 
300V. D.C. . . 
500V. D.C, . . 
760V. D.C. , . 
1SV. AC... 
50V. A.C . . . 



87,6 
87/6 
87/6 
87/6 
27/6 
87,'6 



50-0-50uA .37/6 lamp 27/6 

lOOut 37'6 2 amp 87/8 15V. D.C. . , . S7/B 500 

100-6-IOOM 85- Samp 27/6 20 V. D.C 87/6 Sir 

200,iIa 36/- 20mA 27/6 100V. D.C, .. .27/6 VU 



Full range of other sizes in stock. 



150V. A.C. . . .87/8 

aOOV. A.C 27/6 

500 V. A.C B7f6 

meter lmA.32,'- 

meter 42/- 

Send s.a.c.'for leaflet. 



POWER RHEOSTATS 



High quality commie coic=l ruction. Wiudmgs etobeuded in vitreous 
enamel. Heavy duty brush wiper. Continuous rating. Wide range 
cs-stock Single hole tiling, im. dia. shafts. Bulk quantities available. 
25 WATT. 10;20/a0/ 100, 250/500/1, 000,'1,&00/2,500 or 5,000 ohms, 14/8. P. ■ 
60 WATT. 10/25/80/100/250/o00;i,fKI0/2.500 or 5,000 ohme, 21/-. P. & P. 1/fl 
100 WATT. 1 WlO/flE/oO/lOO.BoO/SOO/l ,000 or 2,500 ohms, 27/6. P » P. 1/6. 




CRYSTAL 




CALIBRATORS Ho. 10 

Small portable crystal 
controlled -vravemeter. 
Siie7*x7i-x4\ Pre. 
quency range 500 Kc/s, 
10 Mc/s (up to 30 Mc/s 
on harmonics). Cali- 
brated dial. Power re- 
quirements 300 V.D.C. 
15mA and 12 V.D.C. 
0.3 A. Excellent con- 
dition. BS/6. Carr. 7/C. 






T.E.40 
HIGH SENSITIVITY 
A.C. VOLTMETER 

10 meg. input 10 ranges: 
■01 / -003 1 -1 .' -3 / 1 / 
3 / 10 / 30 / 100 / 300V. 
R.M.8. 4c,'3.-]'2Me,'s. 

Decibels —40 to 4-50dB. 
Supplied brand new 
complete with leads and 
instructions. Op (nation 
230V a.c. £17.10.0. Carr 




LELAND MODEL 17 BEAT 
FREQUENCY OSCILLATORS 

Frequency 0-J0 Kc.'s on 2 ranges. Output 
600 R orukQ. Operation 2O0/250V. A.C. 
Supplied in perfect order. £12.10.0. Carr. 
10/-. __^ 

TE-65 VALVE VOLTMETER 

High quality instrument 
with 28 ranges. D.C. volts 
10-l.EOOV. A.c. volts 
I 5-1 ,500 V . Resistance 
up to 1,000 megohms, 
220/240V a.c. operation. 
Complete with probe and 
instructions. 117.10.0. 
1'. & F, tj/-. Additional 
Probes available i R.F. 
42/6. D.V. 50/-. 

COSSOR 1049 DOUBLE BEAM 
OSCILLOSCOPES 

D.e. coupled. Band width lkc/s. Perfect 
order. £85. Carr. 30/-. 








AM/FM SIGNAL GENERATORS 

Oscillator Test No. 
2. A high quality 
precision instru- 
ment made for the 
ministry by Alrmee. 
Frequency cover- 
age 20-80Mc/». AM 
u.W./FM. Incor- 
porates precision dud, level meter, precision 
attenuator liiV-lOOmV. Operation from 
12V d.e. or O/1I0/2O0/25OV ax. 91ic 
12;: 8; ::91n. Supplied in brand new 
condition complete with all connectors 
fully tested. 246. Carr, i!0;-. 

RUSSIAN C1-16 DOUBLE 
BEAM OSCILLOSCOPES 

5MHz Pass Band. Separate Yl, Y2 ampli- 
fiers. Calibrated triggered sweep from 
0-2/isee to lOOmsec/cm. 
Supplied complete with all accessories and 
Instructions, 187, Carr. paid. 




EDDYSTONE VHF RECEIVERS MODEL 
J70R. 19-105 Mc/s. Excellent condition. 1180 

TE-18A Trsniiitoriwd 
Sinn si Generator. 5 ranges 
400 kHz-30 mHz. An 
inexpensive instrument 
for the handyman . Oper- 
ates on 9v battery. Wide, 
easy to read scale. 
800 kHz modulation. 
&',-,;51x31l. Complete 
with instructions and 
leads. 17.19.6. P. &?, 4/-. 

TE-1035 STEREO HEADPHONES 

Low cost high 
performance stereo 
headphones. Foam 
rubber ear eupi. 
Adjustable 
headband. 8 ohm 
impedance. 
25-18,000Hz. Willi 
lead and stereo 
jack plug- 
ONLY 39/8. l'.Al'. 




AUTO TRANSFORMERS 

0.1I5;'230v. Step up or step down, 
shrouded. 

150 W. 12,2.6. P. * P. 3,6 

300 W. W.S.O, P. & P. 4/0 

500 W. 14.10.0, P. & P. 6/6 

1,000 W. 10.10.0, P. i P. 7,(1 

1,500 W. 18.19,8, P- * P. 8/0 

7,500 W, 115.10.0, P. & P. 20/- 



Fully 




766 



Practical Electronics October 1970 



■ 



VARIABLE TRANSFORMERS 

i'h.l'. 50'60Hi. Output variiible 



BEHCH MOUHTIHG 
1 nmp, £5.10.0; 2! amp, £6.15.0: 5 in 
£9.15.0; 8 amp, 114.10.0; 10 amp, (18.10.0: 
20 amp, f 37.0.0. 

FAJTEL MOUNTING 
amp, £5.10,0: 2} mnp, £d,lg.B. 




TE-20D RF SIGNAL GENERATOR 
Accurate wide range 
signal generator cover. 
■DS iSOtaspi to 500Mc/s 
OO 6 bands. Directly 
calibrated. Variable 
HP attenuator, audio 
output. Xtal socket 
tor calibration. 220/ 
240 V a,c. Nize 140 :-: 
215 ;. 170mm. Brand 
new with instructions. 
ilS. Carr. 7/6. 



TY75 AUDIO SIGNAL 
GENERATOR 

BGM Wave 20e/& to 
200ke;Si. .Square Wave 
20c/» to 30kc/s. High 
and low impedance 
output. Output variable 
up la ti volts. 220/240 
volts n.c. Size 210 
130 120mm. Brand 

iwH with instruction*. 
111. Cnrr, 7.1. 




MARCO*! TF148B DI9TORTIOX FACTOR 
MITERS, Excellent rendition. Fullv tested. 
ISO. Carr, 16.'-. 



LAFAYETTE TE46 RESISTANCE 
CAPACITY ANALYSER 

2pF- 2,000 mfd 
!i otms-200 

roefobms. Also 
checks mi jit- 
dance, turns 

ratio, insula- 

tion, 20O/250V 
a.c. 

Bnnd few £17.10.0 
C«t. 7/6. 




ADVANCE TEST EQUIPMENT 

Brand new and hosed in original pealed cartoni 

JIB. AUDIO SIOXAI GENERATOR] 

15 c/s to SO Kc/s. Sine ware. Output (100 

ohms or 6 ohms. t30.0.0. 

VM79. tJHf MILLIVOLT METER. 

100 Kc/s to 1,000 Mc/«. a.e. 10 mV to 3 V, 

D.c. 10 raV to 3V. Current 01 /iA to 0-3 

mA. Resistance 1 ohm to 10 megohm. 

£185.0,0. 

TT1S. TBABSISTOB TESTER. Full range ol 

facilities for testing FNP or H 1'N" transistors 

in or out of circuit. 137.10.0. 

Carriage 10/- per item. 




TO-3 PORTABLE OSCILLOSCOPE 

31n. tube. Y amp. Sensiti- 
vity 0'lv p-p/CM. Band- 
width l-o eps-1-5 MHz. 
Input Imp. 3 meg O 25pF 
X amp. sensitivity 0-Liv. 
p-p/CM. Bandwidth la cps 
-300 KHz, Input Imp. 2 
meg a 20pF. Time base. 
S ranges 10 cps-300 KHz, 
Synchronization. Internal/ 
external. Illuminated scale 140 x 215 X 330 
mm. Weight IB J lb. 220/240V. A.C. Supplied 
brand new with handbook. £37.10,0. Can . 10 - 

TSUI. 
DECADE 
R MMTA 8CE 
ATTOTJATOK 

Variable rangt 
0-11 Idli. Con. 
neetions. Un- 
balanced T and Bridge T. Impedance 
000 O range (0 ldB ;■: 10) -f (ldB x 10) 
+ 10 + 20 + 30 + 40dB. Frequency : 

d.e. to 200kHz {— 3dB). Accuracy: 
OOSdB. + Indication dB -: 01. Maxi- 
mum input leu than 4W (50V). Built In 
MOO load resistance with internal/external 
twitch. Brand new 1X7.10.0. F. ;"; t 





latest 




The latest edition (giving full 
details of a comprehensive 
range of HI Fl EQUIPMENT. 
COMPONENTS. TEST EQUIP- 
MENT and COMMUNICATIONS 
EQUIPMENT. Over 230 

pages, fully illus- 
trated and detail- 
ing thousands of 
items — many at 
bargain prices, 
FREE DISCOUNT 
COUPONS 
VALUE 10/- 



SEND NOW- ONI Y7(6 P& Pffo 




GARRARD 



FULL CURRENT RAXKE OFFERED. BRAHD NEW AT FANTASTIC SAVINGS 



1025 steruo £7.19.8 SL72B 

2025T/C stereo £8.17.6 AP75 

40 MKII stereo IB.8.0 SL75 

3000 Bterco £9.19.6 S5L75B 

SP25MKI1 £10.19.9 SL9JSB 

6SLB3 £ll,ie.B A 70/ 11 

RL05B _ £14.19,9 401 
Carriage r/i extra each item, 

T/liAK FilXTHK AND PEKSPHX 

1. For SF25, SL65, sLao. 3000, 20: 

2. For AF75, .SI.73, *L95. £5.19.9 

3. For SP25 etc. to operate with 11 
Carriage 7/fl extra each type. 




£24.19.6 
£18.19,6 
£25.19.6 
£27.1B.6 
£37.10.0 
£11,19,0 
£25, O.O 



COVKKM 

3TC, S03S, lOMi. £4.10,0 



I iit place £5.19.6 

Full range of Garrard :n 



..lil.li I, . 




LAFAYETTE LA-324 STEREO 
AMPLIFIER 

A fine new Hi-Fi Amplifier at low 
cost* 12*5 watts R.M.S. per channel — 
20-20,000 Hz~db. Inputs for Mag or 
Cer Cartridge, Tuner or Auxiliary. 
Output 4-16 Features Headphone 
Sachet, Tape output. Protected output- 
stage. Finish simulated walnut vinyl 
clad metal case black anil brushed 
anodised aluminium front panel, 
lfjr>-3i"'8r. £84. Carr. 7fB. 



MULTIMETERS for EVEM purpose I 




TE-51. KEW 20.0001! 
VOLT MULTIMETER with 
overload protection ami 
mirror scale. 0/6/60.' 120' 
1,200V a.c. 0,3/30/00,' 300/ 
000/ 3,000V i I.e. 0o0^A/12 
/300mA il.e. 0/60K/fl meg, 
iiliin. 92 '6. 1". & F. 2 ■>',. 



MODEL - AS-1O0B. 
lOOKtl.VOLT. Oin.. 
mirror scale. Built- 
in meter protection . 
/ 3 / 12 / 80 / 120 
300 I 000 / 1,200V 
■I.e. 9/6/90/190/990/ 
000 V, a.c. 0/1 Ou i) 
l.i:''W.'3'»tlMA : 12 Amp. 
0/2 K / 200K / 2M '. 
200MB. —20 1» 

+ 17dB. £12.10.0. 

V. A P. 3 9 





MODEL TE-800 20 ,000 O.P.V. 
Mirror scale, overload protec- 
tion. 0/6/,'26/126/l,0OO V.D.C. 
0/10/6 0/230 /1,000 V. A.C. 0/60 
/iA/280 MA. 0:60K/6 meg. 
-20 to -J 62 db. 75/-. 
P. * P. « ; t>. 



MODEL TE-70. 30,000 
O.F.V. 0.'3/lo/a0;3iiN 
600/1 ,200V. d.c. 0/6. 
30 120/ 600 /1,200V. 
a.c. 0/30jjA / 3/30 / 
300mA. 0/I6K/160K' 
1-6M 16mefohiti 

£5.10.0. P. ic P. 3/-. 





TE-900 20,000 Q 
VOLT G1AHT 

MULTIMETER 
din. full view meter. 2 
colour scale, overload 
liroti'ction. 0/2-ii/lO. 1 
250/l,000/6^0«0V a.c. 
/ 23 / 12-5 / 10 / 00 / 
200 / 1,000 / 5,000V 
d.c. / 50(iA ,' 110 / 
100 I 500m A 10A 
■ I.e. 20K / 200K / 20 
M II - £15. P. A P. 5,'-. 




MODEL TE300 30,000 
O-P.V. Mirror acale. 
overload protection, 0/ 
06 / 3 / Ifi / 60 / 300 
1,200V d.c. 0/6/30/120/ 
S00/J.2OOV a.c. 0/80;iA' 
Bin A / 60rnA / 300mA 
000mA. 0,^K/SOK/800K 
8 meg. — 20 to +03rlB. 
£5,19.8. P. A P. 3/-. 



MODEL TE-10A. 20k |) , 
Volt, 0'i5;60/2SQjaOO/2,SOO 
V, d.e, 10/80/100/500/ 
1,000V. a.c. 0/50uA/2-6 
mA./260A. (i.e. 0/6K/K 
megohm. —20 to !22dF. 
10-0, 100 mfd. to 0100-0-1 
mfd. 89/0. P. * P. 2'6. 

LAFAYETTE 

57 Ranee Haw: 

50,000 O.F.V. 

Multimeter. l).c, 

VolU 125 V- 1,000 V 

A.c. Volts 1-5V- 

1,000V D.o. Currcjit 

25(jA-10 Amp. 

Ohms. 0-15 Megn 

dB.— 20 to +SMB, 

Overload Protection. £12.10.0. Carr. 3,0. 





BELGO DA-20 SOLID STATE 
DECADE AUDIO OSCILLATOR 



New high quality port- 
able instrument.Sine 1 Hz 
to 100kHz. Square 20H* 
to 20kHz. Output max. 
+ 10dB (lOkQ). Opera- 
tion 220/240V a.c. 8lie 
2I6mm loOmm 

120mm. 

Price £27.10.0. Carr. 
8/-. 



Practical Electronics October 1970 




MODEL FT-34. 
1.000 O. F.V.0/10' 
50 / 250 / 500 / 
1,000V a.c. and 
d.c. 0.1.I0O/50O 
m A d.c. 0:1 00 
K fl S9 6. 1". & P. 



SAVE UP TO 



33i% 



ON HI-FI EQUIPMENT 
Send for discount price list 




AVO CT471A MULTIMETER 

Battery operated, fully transistorised. 
Sensitivity 100m 0/ v. Measures AC/DC 
Voltages 12mV to l,200v. AC/DC Current 
12uA to 1.2 Amp. Resistance 12 ohm to 
120 raC HF, VHP, TJHF, Voltage with 
multiplier 4v to 400v up to 50 Mefg, 40nlVto 
4V up to 1,000 Mc/e. 

Offered in perfect condition. £56 each. 
Carr. 10/-. 



TRANSISTORISED 
TWO-WAY TELEPHONE 
INTERCOM 

Operative over amazingly 
long distances, separate call 
and press to tallc buttons, 
2-ttire connection. 1000's of 
applications. Beautifully fin- 
ished in ebony. Supplied 
complete with batteries ami" 
wall brackets. 
£8.19.6. P. A P. 3/0. 



SINCLAIR EQUIPMENT 

Project 60. Package offer*. 2 v. Z30 amplifier. 

utereo 60 pre-amp. PZ6 power supply, 
£19.0.0, Carr. 7/9. Or 
with FZ6 power supply, 
£21, Carr. 7/6. -2 M Z50 
amplifier, stereo 60 pre- 
amp, PZ8 power supply, 
£21.10.0, Carr. 7/6. 
Transformer for PZ8, 
59/6 eitra. Add to anv 

■ it the above £4.17.9. Jor active filter unit 

and (18 for it pair of Q16 speakers. 

All other Sinclair products in stock, 2,000 

amplifier, £83, Carr. 7/8. Neoteric amplifier, 

£46, Carr. 7/6. 

PEAK SOUND PRODUCTS 

Full range of Amplifiers, Kits, Speakers in 
stock, 

SOLID STATE VARIABLE A.C. 
VOLTAGE REGULATORS 

Compact and panel mount- 
ing. Ideal for control of 
lamps, drills, electrical 
appliances. etc. Input 
230/240 V a.c. Outputcon- 
tlnuously variable from 
20V to 230V. 

Model MR230S 5 A 68 ^ 46 
A 43mm, £8.7. S. Model 
MR2310 10A SO :- 68 - 
,m. £11.19.8 Postage 2/6. 





HOSIDEN DH-08S DE-LUXE 

STEREO 

HEADPHONES 

Feature* unique mech- 
anical 2-way unite and 
fitted adjustable level 
controls, 8 ohm im- 
pedance. 20-20,000cpa. 
Complete with spring 
lead A stereo jack pluc 
£7.19.6, P.iP.S 






RECORDING HEADS 

C0SMOC0ED i- track heads. High 
hup, reowd/pLiyliark 85;'-. Low imp. 
erase 80/-. MABRIOTT j -track heads. 
High imp. record/playback 84/-. Low imp, 
erase 80/-. Post extra. 

RACAL MA.168 TRANSISTORISED DIVER- 
SITY SWITCH. Brand New Condition 119. 
Carr. 10/-. 

AMERICAN TAPE 

First grade quality American tapes. Brand 
new Discount on quantities. 

Kin, 225ft. L,F. acetate 3/8 

31 In. 600ft. T.P. mylar 1©/- 

Sin. 600ft. std. plastic , 9/9 

5ln. 900ft. L.P, acetate 19/- 

5 in. 1.200ft. D. P. mylar 16/- 

5 Jin. l,20OIt, L.P. acetate IS/9 

5jin. 1,200ft. L.P. mylar 19/- 

5| in. 1,800ft. D.P. mylar 28/6 

5 1 in. 2,400ft. L.P, mylar 39/6 

7in. 1 ,200£t. std. acetate 12/6 

Tin. 1 ,800ft. L.P. acetate 15/- 

71n. 1,800ft. I-.P. mylar 89/- 

Tiu. 2,400ft. D.P, mylar M/- 

7in, 3,600ft. T.P. mylar 45,'- 

Postage 2/-. Over £3 post paid. 

TAPE CASSETTES 

Top quality in plastic library boxes. 
C60 SO min 8/9 3 [or 24/6 
C90 90 min 12/8 3 for 36/- 
C120 120 min 16/- 3 for 43/8 

Cassette Head Cleaner 11/3. All Post Extra. 



G.W.SMITH & CO. ( 




I1TH & CU.I mWM9 LTD 

Z ) 3, LISLE STREET, LONDON, W.C.2 Tel: 01-437 8204 

'»". »■! 34, tISLE STREET, LONDON, W.C.2 Tel: 01-437 9155 

311, EDG WARE ROAD, LONDON, W.2 Tel: 01-262 0387 



TO SATURDAY (EDGWAHE ROAD Vi DAV THURSDAY I 



767 



HOME RADIO (Components) Ltd., Dept. PE, 234-240 London Road, Mitcham, CR4 3HD. Phone 01-64B 8422 | 



Ever had 
kamtafindapa^tis? 



At some time or another most constructors of radio and electronic projects get 
hit by this complaint! The symptoms? Depression , , , exasperation . . . 
headaches . . . weariness . . . sore feet, etc. The causes? Frustrating hours 
spent in thumbing through inadequate out-of-date catalogues, making 
numerous fruitless phone calls, tramping or touring from shop to shop — all in 
a vain attempt to locate some vital components. 

Here is the answer to the problem — the Home Radio Components Catalogue, 
a world renowned medicine for preventing the complaint or for quickly clearing 
up the trouble if symptoms have already begun to appear! Just send the 
coupon with 8/6d plus 4/- postage and packing, and your copy will be 
despatched immediately. In its 350 pages over 8,000 components are clearly 
listed, over 1,500 of them illustrated. A cross-reference Index and a 30-page 
Price List enable you to locate your components without any trouble. 




HOMtR* * ^ 



badio 

MENTS\ LTO 



COMPONENTS! 




Once you have your Home Radio Catalogue you 
c'an, if you wish, make life even easier for yourself 
by joining our Credit Account Service. Then 
you can order by telephone any time of day or 
night, Sundays included! No need to bother with 
postal orders, cheques, registering envelopes 
every time you order. We send prepaid envelopes 
and only one payment is required each month. So 
simple! Write for details or telephone 01-648 8422. 



POST THIS COUPON NOW 
with your cheque or P.O. for f2j6 




The price of 12/6 applies only to catalogues 
purchased by customers residing in the U.K. 



Please write your Name and Address In block capitals 

Name — 



Address- 



iFfr 



HOME RADIO (COMPONENTS) LTD., Dept. PE 

234-240 London Road, Mitcham, Surrey, CR4 3HD 



768 



Practical Electronics October 1970 



VOL 6 
October 



No. 10 
1970 



PRACTICAL 



ELECTRONICS 



Editor P. E. BENNETT Assistant Editor M. A. COLWELL Editorial Assistants D. BARRINGTON G. GODBOLD M. KENWARD 

Art Editor J. D, POUNTNEY Technical Illustrators J. A, HADLEY P, A. LOATES 

Advertisement Manager D. W. B. TILLEARD 



THE IG INVASION 



The British IC industry is worried. Justly, so, for 
three-quarters of the U.K. market for these devices 
has been captured by American companies. The four 
indigenous IC manufacturers have the remaining quarter 
of this market to divide between themselves; and their 
hold on even this fraction is far from secure. In fact, one 
firm seems on the point of throwing in the towel. The 
head of the Mullard Organisation has openly confessed 
his company's inability to produce IC devices at prices 
comparable with those of U.S. competitors. The other 
three home IC makers have not been so forthcoming. 
But there is little doubt that despite the shot in the arm 
provided by the British taxpayer, this trio on which 
Mintech based its main hopes for the future of U.K. 
microelectronics, is feeling the same cold blasts from across 
the Atlantic. 

Allegations of price cutting and dumping have been 
voiced aloud. Governmental action to limit the number 
of IC devices imported has been urged. But can such 
extreme measures really help in the long run? Electronic 
equipment manufacturers in other countries will continue 
to use the more favourably priced devices. Their finished 
products will thus have built-in price advantages over 
similar type products produced in this country and using 
mainly all-British components. 

Protection of the home IC industry cannot conceivably 
benefit the home electronic equipment industry. The 
big question surely is, which branch of the electronics 
industry is the more valuable national asset and has the 
best chance in the future against increasing world-wide 
competition. 

If the hard economic realities are indeed against the 
home IC maker, it might be just as well to bow to the 
inevitable and, instead, capitalise to the full on this 
country's skills in designing and building equipment- 
selecting the best available components from an open 
competitive market. 

This certainly is a form of exercise familiar enough to 
many Practical Electronics readers — to introduce a 
more homely slant into this topic. . . . After all, the 
amateur market is to a great extent a microcosm of the 
professional or industrial market. The advertisements of 
component retailers reflect trends in the bigger world 
outside. Thus readers who have been studying the com- 
ponents listed in these announcements will not have been 
taken by surprise by the IC industry's recent desperate 
cries for help. Clearly, the invasion by U.S. manufac- 
turers has resulted in great price reductions in a variety 
of IC devices. 

We all like to support home industries. But without 
these "foreigners" the amateur's chance to gain experience 
in the vital area of microelectronics would be severely 
curbed. f.e.b. 



THIS MONTH 



CONSTRUCTIONAL PROIECTS 



TELESCOPE TRACKER 770 

LIGHT OPERATED SWITCH 775 

PROTON MAGNETOMETER 782 

TRIAC LAMP REGULATOR 810 



SPECIAL SERIES 



MAKING THE MOST OF 

LOGIC ICs— 4 818 



GENERAL FEATURES 



AUDIOMETRY 804 

INGENUITY UNLIMITED 825 



BEGINNERS 



THERMISTOR THERMOMETER 794 

THIS WAY TO 
ELECTRONICS— 7 



796 



NEWS AND COMMENT 



EDITORIAL 


769 


AUDIO TRENDS 


778 


ELECTRONORAMA 


802 


SPACE WATCH 


809 


NEWS BRIEFS 


822, 826 



Our November issue will be published on 
Thursday, October 15 



fr!HS.!?A & *™A eS Lim '5 ed ! 970 - c ?P? ri 8ht «n a" drawings, photograph* and articles published in PRACTICAL ELECTRONICS is fully 

PRACTrCA^ELECTRON?r^ n !:„r ,W rh 0,1S t ^°' e ^ 5*" are ** preSsly f ° rbid ^- All reasonable precautions are taken by 
PRACTICAL ELECTRONICS to ensure that the advice and data given to readers are reliable. We cannot, however jruarantee it and 

Practical Electronics, Fleetway House, Farring'don St., London, E.C.4. Phone: Editorial 01-634 4452; Advertisements 01-634 4202 




1 Electronics October 1970 



769 



The Moon Probe programme and the startling 
astronomical developments over the last few years 
have created such interest that many people have bought 
small telescopes. Though a small instrument of up to 
3 inches diameter is capable of satisfying the needs of 
most amateurs, half its potential is lost without adequate 
means of synchronously tracking the moon, planet, 
satellite or star under view. 

This article describes the construction of a compact 
and relatively inexpensive drive unit using a mains type 
synchronous motor, driven from a constant frequency 
generator designed for 12 volt operation (batteries or 
mains unit), that can easily be fitted to tripod telescopes 
to provide tracking facilities. The system can also be 
used for larger telescopes with equatorial mountings. 

TRACKING 

The apparent motion of the stars about the north pole 
star is 360 degrees in 24 hours, or 15 degrees per hour; 
this figure is better appreciated in terms of sun or moon 
widths of approximately 05 degrees. The moon 
moves by its width every 2 minutes and since the 
optical gain or magnification of a telescope increases the 
apparent speed, it follows that high magnifications 
require constant use of slow motion controls to keep the 
object in view. Most small telescopes are fitted with a 
slow motion slewing control in the form of a knurled 





knob, spring loaded against backlash, that has a rate of 
about 0*5 degrees per revolution and a total slew of 
approximately 20 degrees. 

Mains type synchronous motors fitted with reduction 
gearboxes are available on the surplus market, with a 
final speed of 0-25 to 4 revs per minute. Such a motor 
is fitted to the telescope frame and coupled to the slow 
motion knob by means of accurately fitted high quality 
gears to give a slew of approximately 15 degrees per 
hour with the motor energised at 50Hz. Using the 
circuit to be described the motor speed can be varied 
accurately by changing the frequency of the supply. 
Adequate torque is available from the motor to rotate 
the telescope and an anti-backlash device can be used, 
e.g., centre sprung double gears. 

FREQUENCY GENERATOR 

A hybrid unijunction bistable circuit is used for the 
frequency generator because: 

(1) The timing stability is excellent being dependent 

upon O and R t according to / = y r r ( wnere f 

represents frequency). 

(2) The stability is independent of transistor parameters 
and is reasonably independent of supply voltage 

changes. 

(3) The timing capacitor G, may be quite small (01 to 
0'22/fFd) and the inexactitude and variations of 
elect roly tics are avoided. 

(4) The frequency may be readily and continuously 
varied over a wide range by changing only one 
component — Rt, and temperature compensation (if 
required) can be easily applied. 

(5) An equal mark to space ratio of well shaped 
rectangular wave form is obtained to feed a step up 
transformer. 



770 



Practical Electronics October 1970 



The behaviour of the unijunction transistor is shown in 
Fig. 1. The capacitor C t charges until the emitter 
voltage is approximately 60 per cent of the voltage 
across bl, b2 (peak point) when the emitter to bl 
junction becomes almost a short circuit and the 
capacitor rapidly discharges. 

TRACKER CIRCUIT 

The unijunction transistor operating as described 
above fires the bistable circuit (Fig. 2) which is fitted 
with speed up capacitors C2 and C3, producing a 
rectangular waveform at the collectors of TR3 and TR5. 
Emitter followers TR2 and TR6 pass this waveform, 
via reverse voltage protective diodes Dl and D2, to the 
bases of TR1 and TR7 which perform a switching 
action and can therefore control powers of approxi- 
mately 5 times that of the normal class A operation. 

The emitter resistors Rl and R15 dissipate some 
useful power and reduce output voltage but apply local 
feedback to linearise the waveform and prevent thermal 
runaway. The values of R 1 and Rl 5 may be varied to 
increase efficiency or reduce current drain as desired; 
changing R3 and R13 to vary the base drive. 

The collectors ofTRl and TR7 are connected to the 
centre tapped secondary winding of a small mains 
transformer Tl ; in this circuit the secondary winding is 
used as a primary. The primary winding forms a 
tuned secondary, the output of which feeds the syn- 
chronous motor to track the telescope. 




Peak point voltaqe 



ov 



Fig. L Unijunction oscillator basic circuit and curve 
showing voltage variation across C, 



UO.5H0.5A 




Fig, 3. Mains power supply for the telescope tracker 

POWER SUPPLY 

The circuit needs approximately 200mA at 12V d.c. 
and this can be supplied from a bank of U2 cells, an 
accumulator or alternatively from a simple mains power 
supply as shown in Fig. 3. In the mains supply circuit 
VRJ is adjusted to give 12 volts output on load and the 
choke LI and capacitor CI are resonated at mains 
frequency. 




Fig. 2. Circuit diagram of 
the telescope tracker 



O.ZSto06uF(M«t«t) 230VOO &Z50V 



4 0V 9V L 




Practical Electronics October 1970 



771 



CONSTRUCTIONAL DETAILS 




COMPONENTS 



Resistors 

R! 6H(2 



R2 

R3 

R4 

R5 

R6 

R7 

R8 

R9 

RIO 

Rll 

RI2 

R 13 

RI4 

R15 

RI6 

RI7 

pig 

All iW carbon 5% 



120 in parallel) 



l-2kO 
2-4kO 
560 Q 
ISO 

200 a 
iika 
iika 
iika 
300 a 
iika 

56012 

2-4ka 

l-2kO 

6a (2 x 12a in parallel) 

approx. 20k Q "1 

approx. 30k a Hsee text) 

approx. 30kaJ 




* T19V ftOVct 

sum* 



T1$V 



Fig. 4. Layout and wiring of the printed circuit board 

FRONT PANEL WIRING 



Potentiometers 

VRI 20kO carbon preset 
VR2 1 0k Q carbon preset 
VR3 20kO carbon lin. 

Capacitors 

CI OI^F-O-22/xF (see text) 

C2 0-0l^tF polyester 

C3 0-OI/tF polyester 

C4 IQO/aFelect. 15V 

C5 0-25,*F-0-6/iF 450V (see text) 

Semiconductors 

Dl OA202 

D2 OA202 

TRI BFY50 

TR2 2N3702 

TR3 2N3702 

TR4 2N2646 (unijunction) 

TR5 2N3702 

TR6 2N3702 

TR7 BFY50 

Switches 

51 3-way wafer 

52 single-pole on /off toggle 

53 single-pole on off toggle 




For detail; of wiring to 
this panel set inset 

\ 



Miscellaneous 

Tl Mains transformer 200/250V primary 9V-IV9V 

secondary — used in reverse (Douglas L.T. type) 
M0I Synchronous mains motor, 0-25--4 r.p.m. 
Printed circuit board, metal case, gears 




Printed circuit 
board mounted 
jS on4-3£lono, X 
* 6BA Spacers 



toMOt 



Fig. 5. Wiring diagram of the components mounted inside 
the tracker case 



772 



Practical Electronics October 1970 



J- 






CONSTRUCTION 

Most of the components are mounted on a printed 
circuit board, shown full size in Fig. 4. The board is 
fitted, together with the output transformer (Tl), C5, the 
controls and associated resistors, inside a metal case of 
suitable size. A layout and wiring diagram of the 
components inside the case is shown in Fig. 5. The 
mains or battery supply is accommodated outside 
the case as is the tracking motor MOl. 

When the telescope is tripod mounted and has a 
slow motion tracking screw the motor may be geared 
directly to this screw and hence revolve the telescope 
through an angle of some 20 degrees. The coupling 
gear ratio can be ascertained by calculation of the 
number of revolutions of the tracking screw to swing the 
telescope through 15 degrees. Assuming the speed of 
the motor is known the gear ratio can be found in the 
following manner 



Gear ratio = molor speed in rev, per min. x 



60 



revolutions of tracking screw required for 
1 5 degree swing 
Assuming the motor speed to be 0-5 r.p.m. and that 
15*5 turns of the slow motion screw produce a 15 degree 
swing of the telescope the gear ratio required is: 

0-5.60 ™, lcc 
— — - or 30/15-5 

Since this is almost 2/1, gears of that ratio may be 
used and the slight error will be easily compensated by 
frequency adjustment in the circuit, 

TESTING 

The circuit should be set up with a polyester capacitor 
of 0-22/tF as CI and a 100 kilohm resistor as Re, the 
output waveform is examined on an oscilloscope and C5 
adjusted until the waveform is as shown in Fig. 6b. If 
an oscilloscope is not available then the transformer 
should be resonated, with the load applied, by monitor- 
ing the output voltage with a voltmeter (approximately 
1 80V r.m.s.) and adjusting C5 in fine increments for a 
maximum reading. 

Use should be made of the primary tappings of the 
transformer (if available) not only to achieve the required 
output but to incrementally change the effect of C5. 

Practical Electronics October 1970 



Fig. 6a indicates an output waveform without C5 and 
Fig. 6c shows a waveform with the transformer 
resonated for 50Hz but with the generator frequency 
changed. 



300 V 





Fig. 6. Graphs of output voltage (a) without C5, (b) in 
resonance, (c) with transformer resonated for 50Hz but 
with the generator frequency changed 






Off tune waveform 
50V per division, 
130V Avo monitor 



On tune waveform 
50V per division, 
140V Avo monitor 




Fig, 7. Control circuit used to replace Rt in telescope 
tracker circuit 



The output frequency should be accurately deter- 
mined by connecting the generator to a household 
electric clock and noting the timing error over a period 
of hours. If this frequency is not close to 50Hz Rt 
should be changed and C5 readjusted. Finally, with 
CI and C5 set for 50Hz replace Rt with a variable 
resistor to slow the frequency until the drive motor to be 
used will no longer start up on load: this value of Ri 
should be measured as R\ s i w; similarly determine the 
upper limit Rt rast. The output voltage should be at 
least 150 volts r.m.s. in the slow and fast condition 

dependent upon Rl and R15. 
r 

CONTROL CIRCUIT 

The timing resistor Rt is replaced by the circuit of 
Fig. 7. Switch S3 (slow) is normally closed, and when 
S2 (fast) is closed resistor combination R X2 has the value 
Of Rt fast. The variable resistors VR1, VR2 and VR3 
are chosen and adjusted for star, moon and auxiliary 
rates and switch S3 is used to introduce i? (1 such that 
/ft, + Jit. + VR1 (etc.) = Rt slow- The thermistor in- 
dicated may be used to shunt part of J?t 2 to give tem- 
perature compensation (if required) for the temperature 
coefficient of CI (of the order of +300 parts per million 
per degree centigrade). 

FINAL SETTING UP 

Direct the telescope to a bright star group and use the 
fast and slow switches to centralise the group such that 
stars can be observed on the edges of the field of view. 
Preset VR2 is adjusted until the group is synchronously 
tracked. Repeat the above procedure using the moon, 
which moves relative to the stars, and adjust VR1 using 
a prominent crater as a marker. The remaining 
variable resistor VR3 is fitted with a suitable knob and 
used to track satellites, etc. 

If the drive is fitted to a telescope, with an equatorial 
mount, as a 360 degree drive, the adjustment of VR2 
can be accurately set by leaving the unit powered and 
performing a 24 hour check, preferably with the 
generator kept indoors at a reasonably constant 
temperature. The degree of temperature compensation 
can then be determined by noting the angular error over 
24 hours for a given temperature change and deter- 
mining the necessary change in the value of i?t to 
correct this. It will be found that a thermistor that 
changes from, say 10 kilohms to 3 kilohms (0 degrees C 
—30 degrees C) can be used as indicated in Fig. 7 to 
compensate for the change in value of CI. *^ 



774 



Practical Electronics October 1970 



ByT.F.Carruthers 



The circuit to be described was designed to operate a 
bench light when the daylight fell below a certain 
level. The unit was to switch sharply and accurately 
at the same light level each time, to avoid repeated 
setting and interactions between the light sensor and 
the switched light when switching begins. 

CIRCUIT DESCRIPTION 

To ensure accurate switching an amplifier with high 
impedance must be used to amplify current taken from 
the voltage developed across the light dependent 
resistor (Fig. 1). A common collector amplifier is 
used, the first transistor (TR1) is a silicon device to 
prevent leakage current affecting the voltage across the 
kd.r. (XI); all leakage current passes through Rl. 
Transistor TR2 need not be silicon, an OC71 would do, 
but an OC200 is used to prevent variations in switching 
due to temperature variations. Theoretically the 
input impedance of the stage is /tfe 2 /?i so that for 
circuit used the input impedance should be of the order 
the of 160 megohms for an /?fe of only 40. 

Transistor TR3 is the power switch and is an npn 
device, in order to improve the switching time positive 
feedback is applied by R4. The feedback resistor 
couples the collector of TR3 to the base of TR1. 



When light is falling on the l.d.r. TR3 is off and the 
only effect of R4 is to shunt the l.d.r. ; once the voltage 
at the l.d.r. rises to a sufficient level, due to failing light 
causing its resistance to rise, TR1 starts to conduct and 
the collector voltage of TR3 begins to rise. This 
voltage rise at TR3 collector is fed back via R4 and 
since the impedances around the base of TR1 are large 
in value then the voltage drop across R4 is small and 
the base voltage of TR1 rises causing TR1 to switch 
fully on. The regenerative effect ensures rapid 
switching. 

Zener diode D6 is used to supply a constant voltage 
to the emitter of TR2; this stabilises the switching 
voltage required at the base of TR1. If a Zener diode 
is considered an expensive luxury, then it is possible to 
change VR1 to 100D and omit D6. This will reduce 
the accuracy of the switching and the level at which the 
device switches will be more dependent on variations of 
supply voltage. 

POWER SWITCHING 

The switching operation is performed by a thyristor 
with a voltage rating of 350 volts or more at 0-5A. 
Resistor R7 may need to be changed if the specified 
thyristor is not used. 



-«v 




^\AA 

R4 100kfl 

Fig. I. Circuit diagram of the light operated switch for 
use with a 12V supply and 12V had 




Fig. 2(a). Current supplied to load when a.c. is applied 
directly across the thyristor. (b) Current supplied to load 
when full wave rectified 



Practical Electronics October 1970 



775 



To switch on the thyristor it is necessary to supply a 
pulse of current to the gate of the device, this is done by 
switching TR3. To switch off the thyristor the load 
current must be reduced to a low level, typically 10mA, 
If the thyristor is fed from an a.c. source the load current 
is reduced to zero every half cycle. Unfortunately 
such a system would supply half wave rectified power 
(see Fig. 2a) to the light and this causes a flickering effect 
which can be disconcerting. This may be avoided by 
full wave rectifying the mains before feeding it to the 
thyristor (Fig. 2b). A full wave rectified mains supply 
circuit is shown in Fig. 3. 

If the unit is required to switch off when the light 
level increases, CI should be omitted from the supply 
circuit (Fig. 3). For most uses it is better that the 
light should remain on, independent of changes in light 
level, this allows the l.d.r. to be placed on the workspace 
to be illuminated. Also if the l.d.r. is placed in a 
window headlamps from cars passing may cause the 
unit to switch unless it locks on. 

Capacitor CI will maintain the current to the load 
above the thyristor holding current (see Fig. 2), the 



value given is sufficient for use with a load of up to 
200 watts, for greater loads a value must be determined 
by trial and error. The current rating of CI is 
important, this can be calculated by: 

load power 
max. surge current = supp i y voltage 

RELAY OPERATION 

A relay may be used in preference to a thyristor for 
switching the load as shown in Fig. 4. If a relay is used 
its coil resistance must be greater than 150H to, prevent 
the current through TR3 becoming excessive. If the 
coil resistance is less than this, but the relay only 
requires 100mA or less to operate, then R6 may be 
replaced by a resistor of sufficient value to limit the 
current through TR3 to 100mA or less. The relay 
should be wired to latch on (see Fig. 4). 

When a relay is used it is not necessary to rectify the 
mains before supplying the load as the contacts will pass 
the full waveform to the load; this represents a con- 
siderable saving in cost of diodes. Diode D7 protects 
TR3 from the back e.m.f. generated when the relay is 




Fig. 3. Circuit of a mains supply using two transformers 
and full wave rectification of the 250V load supply 




RLA 
Z 



w 



D7 

.QAZCO 



i , m — 1 1,0 A 200 

J—, i^ ■ » 

5onl 1 " a _ L 



: l a 



RLA2 



TO 

^LOAD 



Fig. 4. Modified circuit using 
a relay to switch the load 



ll 2345678 



SCSI 

, « , LOAD 

EARTH CATHODE GATE ANODE r-*—. 

t f t-Jf 

8 9 10 11 12 U 15 16 17 16 19 I ^ 

O A O • A * *\A » o O •, • f 




Eg SEOOiBWff 
250Vq.c. 



T2 SECONDARY 
(12 Vox.) 



» • o o"'6"o"'o O o "«'«'»' • &&"♦ " JTlp ^- ftj • '♦' '•'"• 
«.«t^\ | i!-.^"M.'y..-/ , -\ ■■■-'■ - ' .-y.- ^^r:.":.-" •-.:•■:??■■----■.■.■■ ■ ; --i/'-- y J^::JEZnzzi":.: 



— --TT-, ,.. . ■■■: .. 



— ■ -'. V: -■--,,..■■-. ■■,.-■,■■- ■■-,-W>.-. 






• (< $•• • fa) • * • ( 6;:f A • • _• 

■ ■ " * "'. Z ■■■-■■ ■■■. " - ■:■ ~- .. - ■■--■ --■■"■■ ■■ ■:■: 



TW* 



• •O«00»0»0 9 C • • • * 



Jj oi c 



• • • • 



Fig. 5. Veroboard layout and wiring of the mains supply and mains load switching light operated switch (see text> 

776 Practical Ekctroftics October 1970 




de-energised. Contacts RLA1 latch the relay on and the 
circuit must then be disconnected from the supply to 
turn the load off. For non-latching operation RLA1 
contacts can be omitted. 

CONSTRUCTION 

The circuit is assembled on a single piece of Vero- 
board as shown in Fig. 5. Transformer Tl, VR1, XI 
and the thyristor can be mounted around the Vero- 
board in a small metal case. When a mains supply is 
used an adequate earth must be provided to the Vero- 
board and the metal case. 



COMPONENTS 



Resistors 

Rl lOOkQ 

R2 I2kn 

R3 4-7kfi 

R4 iOOkO 

R5 220 Q 

R6 l2kQ 

R7 330fl\ „„„ „ . 

R8 560 fi f required for relay version 

AH ±10%, £W carbon 

Capacitors 

CI 8fzF elect, 250V \for mains supply version 
C2 200^F elect. 15V /only 

Semiconductors 

TRI OC200 
TR2 OC200 
TR3 AC 1 27 
D6 IS202 (4-7V Zener diode) 
SCR I CRSI/40 not required for relay version 
DI-4 BYIOOT 
D5 DD000 y or mains supply version only 
orDD003j ' 

Miscellaneous 

XI ORPI2 photocell 

VRI 500Q carbon potentiometer 

RLA 12V I50Q relay with two pairs of normally 

open contacts, one pair rated at 250V I A (see text 

—for relay version only) 
Tl Mains isolation transformer"! 

— I00W I for mains supply 

T2 Mains transformer: secondary f version only 

12V 05A J 

Veroboard, case 



Practical Electronics October 1970 



If a battery is used to supply the circuit, components 
Dl-5, CI and C2 can be omitted from the Veroboard 
and the connections to Tl secondary (12V a.c.) con- 
nected to the supply— make sure that the negative line is 
applied to the strip A on the board. The breaks at 14F 
and 17-18,4 should not be made when a battery supply is 
used. All wires carrying mains voltage should be 
insulated and of sufficient size to carry the load current. 

Once complete the unit can be tested by connecting 
a load and varying the light falling on XI; VRI is 
used to set the switching level. 

LOAD POWER 

Load power is limited by Tl rating, Dl-4 rating and 
the thyristor rating. Using the components specified 
the load power is limited to 100 watts by Tl. When a 
battery supply is used the load power is limited only by 
the thyristor and for a 12V supply would be 12 watts, 
this power could be increased by using a thyristor with a 
higher current rating. 

When switching inductive lamps the thyristor should 
be able to pass the cold resistance current— normally 
about twice the normal current. 

If the relay circuit in Fig. 4 is used, Tl can be omitted 
and the supply fed from T2 and D2 or a battery. The 
relay contacts RLA2 should be rated at 250V a.c. I amp 
for a 100W load or at higher current ratings for 
increased loads. 

APPLICATIONS 

The switch unit is very versatile and may be used for a 
number of jobs; the switch will operate mains lamps or 
car parking lights. When used for the second of these a 
non-latching relay should be employed and the l.d.r. 
sited away from the switched lights and from any other 
source of artificial light. If protection against shadows 
falling across the l.d.r. or momentary illumination is 
required a capacitor can be placed across the l.d.r. 
the value of which is best found by trial and error— too 
large a value should be avoided as this would slow down 
the switching speed— 10/tF is a good value to use as a 
starting point. 

The switch may also be used as a burglar alarm; if 
the unit is arranged so that a thief interrupts a beam of 
light falling on the l.d.r., the switch will power an 
alarm that can be locked on to indicate an intruder. 
The light beam may be made invisible by the use of an 
OCP71, in place of the ORP12, and an infra red light 
source. Any bulb with an infra red filter may be used 
and the beam focused on the sensitive section of the 
OCP71. jL 



777 




By F.C.JUDD 



Once again an audio products exhibition is with us 
and what was formerly the International Audio 
and Photocine Fair is now the International Audio and 
Music Fair to be held at Olympia from October 
19 to 24, with trade only day on the October 19. 

Why has "music" come into the name of the 
exhibition? Many may be wondering for example if 
the exhibition has been extended to cover electronic and 
other musical instruments. In fact it has not and 
"music" denotes general interest in music reproduction 
which is to be promoted by approximately 20 special 
presentations during the course of the exhibition in the 
form of music recitals and lectures. 

The organisers also hope to present the Moog 
Electronic Music Synthesiser with demonstrations of its 
capabilities. The fact remains however, that a com- 
bined audio and musical instrument fair might prove as 
successful in this country as the annual "Firato" 
exhibition in Holland. 

SONEX 71 

Following the successful Sonex '70 exhibition at the 
Skyway Hotel (Nr. London Airport) last April, the 
organisers, British Audio Promotions Limited, have 
now decided to run "Sonex '71" at the same venue. 







The Daystrom (Heathkit) Audio Signal Generator 
(sine or square wave) type AO-/U 



The dates have been announced as Wednesday, March 
31 to Sunday, April 4, 1971 with the first (wo days for the 
trade only. 

Two whole days for trade visitors only, was 
apparently supported by a large majority of exhibitors. 
The number of exhibitors at "Sonex '71" is expected to 
be not less than 60. 

AUDIO TEST EQUIPMENT 

No new audio products with any significant develop- 
ments have been announced Since Sonex '70 and the 
time of writing is too early for notice from manu- 
facturers of anything outstanding they are likely to be 
showing at Olympia. For this reason most of this 
month's Audio Trends is devoted to a few items of 
currently available audio test equipment which may 
well be of interest to those who construct a good deal of 
audio equipment and have little time to build their own 
test gear. 

Accurate test equipment is, of course, invaluable in 
all applications of electronics and particularly in the 



Since this article was prepared 
the name Daystrom has been 
superseded by Heath-Gloucester 
Ltd. 



The Daystrom Model AV-3U 
audio millivolt meter 








The Daystrom 
Model OS2 
general purpose 
oscilloscope 



design and development of circuitry. In audio work 
the two main essential instruments are perhaps the 
audio signal generator and the oscilloscope. An 
oscilloscope with reasonably accurate calibration can 
be used to measure audio signal amplitudes as well as 
show defects and distortion. 

The ideal combination is a signal generator, oscillo- 
scope and audio millivolt meter. A distortion meter 
might be considered a luxury as far as the amateur 
equipment constructor is concerned but is an essential 
piece of equipment in a design laboratory. 

TEST GEAR IN KIT FORM 

The greatest problem in building one's own test gear 
is that of reasonably accurate calibration, for unless 



778 



Practical Electronics October 1970 



VARIABLE VOLTAGE TRANSFORMERS 



LIGHT SENSITIVE SWITCH 

Kit of parts, including ORPI2 Cad- 
mium Sulphide Photocell, Relay* 
Transistor and Circuit, etc, 6-12 
volt D.C. op. price 25/- plus 2/6 
P. & P, ORP 12 including circuit, 
12/4 each, Post Paid. 
A.C. MAINS MODEL. Incorporates 
Mains Transformer, Rectifier and special 
relay with 2x5 amp mains, c/o contacts. 
Price inc. circuit 47/6 plus 2/6 P. & P. 

LIGHT SOURCE AND PHOTO 
CELL MOUNTING! 

Precision engineered 

light source with adjustable 

lens assembly and ventilated 

lamp housing, to take MBC bulb. Separate 

photo cell mounting assembly for ORP. 12 

or similar cell. Both units are single hole 

fixing. Price per pair £2.15.0. P. & P. 3/6. 

UNISELECTOR SWITCHES 
NEW 

4 Bank 25 Way 24V d.c. 

operation £5.17.6, P. & P. 2/6. 

6 Bank 25 Way 24V d.c, £6.10.0. p.p. 2/6. 

8 Bank 25 Way 24V d.c. operation. 

£7.12.6 plus 4/6 P. & P. 



RPI AYQ New SIEMENS, 
rvcL -" ■ *■* PLESSEY. etc. miniature 
relays at COMPETITIVE PRICES 

Contacts Price 



Coil Working 

(1 d.c. Volts 

51 6-9 6M 

230 6-12 2c/o 

280 6-12 2 c/a 

700 1 6-24 -4M 2B 

1250 36-45 6M 

2500 36-45 6M 

5800 80-85 4 c/o 

9000 40-70 2 e/o 



12/6 

12/6 

I.E. 14/6 

LB. 12/6 

12/6 

12/6 

12/6 

I.E. 10/- 



H.D. Heavy Duty. POST PAID 
IB. = lncluding Base 





T.M.C ILLUMINATED LOCKING 

PUSH BUTTON KEY SWITCH 

No. $.525594 Lock 4 c o 

Complete with mounting 

bracket, push knob and 

lenses (green, amber, red 

or clear — state colour 

preference). 

Price I4.'6 each excluding 

bulb, post paid. Discount for quantities of 

200 and over. 

i^e"ctr"onic organ kit 

Ideal present 
for Electronically 
minded boy. 
Easy to build. 
Solid State. Two full octaves 
(less sharps and flats). Fitted hardwood 
case. Powered by two .penlite .1 Iv 
batteries. Complete set of parts including 
speaker, etc. together with full instructions 
and 10 tunes. Have all the pleasure of build- 
ing .this instrument and finish with a 
functional and instructive gift for any boy 
or girl. Price £3.0.0. P. & P. 4/6. 

TWO* pToDEL48A """ 

ix-Admiratty in good condition with instruc 
tions, leads, plus D.C. Shunts for 120 Amp 
and 480 Amp. A.C. Transformer for 60 Amp 
and 240 Amp. Multiplier for 3600 volt. Com 
piece outfit in fitted case. £15 0, P. & P. 10 - 

"Tttransformers 

All primaries 220-240V 

Type No. 5ec. Taps Price Corr. 

1 12V at 5 A £1.17.4 5/6 

2 30. 32, 34, 36V at 5 A . . £4.13.4 6/ 

3 30, 40, 50V at 5A £6.17.6 6/6 

4 10, 17, 18V at I0A ....£4.19.0 4/6 

5 6, 12V at MA .£4,6.9 6/6 

6 17, IB, 20V at 20A £7.5.9 6/6 

7 6. 12. 20V at 20A £4.17.6 7/6 

8 24V at I0A £5.4.6 S/6 

9 4, 6, 24. 32V at 1 2A . . £7.3.0 6/6 



INPUT 230/24OV. A.C. 50/60 
OUTPUT VARIABLE 0-260v. 
BRAND NEW 

Keenest prices in the country. 
All Types (and Spare*) from 
1 to 50 amp. from stock. 

SHROUDED TYPE 

I amp, £5. 10. 0, 2.5 amp*, 
£6. 15. 0. 5 amps, £9. IS. 0. 
8 amps, £14. 10. 0. 10 amps, 
£18. 10. 0. 12 amp*, £21. 0. 0. 
15 amps, £25. 0. 0. 20 am pi, 
£37. 0. 0. 37.5 amps, £72. 0. 0. 
50 amps, £92. 0. 0. 
OPEN TYPE (Panel Mounting) 
| arnp, £3.18.6. I amp, £5.10,0. 




2 j amps, £6.12.6. 



STROBE! STROBE! STROBE 



Build a Strobe Unit, using the latest type Xenon 
white light flash tube. Solid state timing and trigger- 
ing circuit. 230/250v. A.C. operation. 

EXPERIMENTERS' ECONOMY KIT 

Speed adjustable I to 36 Flash per sec. All electronic 
components including Veroboard S.C.R, Unijunction 
Xenon Tube and instructions £5.5.0 plus 5/- P. * P. 

NEW INDUSTRIAL KIT 

Ideally suitable for schools, laboratories, etc. Holler tin 

printed circuit. New trigger coil, plastic thyristor. 

Speed adjustable 1-80 f.p.s. Price 9 gm. 7 6 P. & P. 

HY-LYGHT STROBE 

This strobe has been designed and produced in response 

to wide public demand, for use in large rooms, halls and 

the photographic field, and utilizes a silica plug-in tube 

for longer life expectancy, printed circuit for easy 

assembly, also a special trigger coil and output capacitor. 

Speed adjustable 0-30 f.p. s. Light Output approx. 4 joules. 

Price £10,17.6. P. & P. 7/6. 

7-inch POLISHED REFLECTOR 

Ideally suited for above Strobe kits. Price 10/6. P. & P. 2/6 

or Post Paid with kits. 



,'mTI POAER RHEOSTATS (NEW 



AVAILABLE IN THE F0LL0WIN6 VALUES: 

I ohm, 10 a.; 5 ohm, 4.7 a.; 10 ohm, 3 a.; 

25 ohm, 2 a.; 50 ohm, 1.4 a; 100 ohm, I a. 

250 ohm, .7 a.; 500 ohm, .45 a.; I Kohm, 

280 mA; I '5 Kohm, 230 mA;2'5 Kohm, .2 a; 5 Kohm, 140 

mA. Diameter 3Jin. Shaft length Jin., dia. H'm. All at 27/4 

each. P. & P. 1/6. 

50 WATT. l/5/IO/2S/50/IOO/250/500/l/l'5/2'5/5Kohm 

All at 21 /-each. P. & P. 1/6. 

25 WATT. 1 0/25/50/ 1 00/250/500/1/ 1 -5/2'5 Kohm. All 

at H/6each. P. & P. 1/6. 

VEEDER ROOt7230V a.c. 50 cycle, 5-ftgure 
counter (non-resettabie). I S/6 , P. & P. 1/6. ^|8 

nTckIl cad. batTery ouTfrT't'ErWl).) 

Two metal carrying cases each containing 10 >: I-2V 7AH (12V) 

Batteries, also 10 X I 2V 22AH (12V) 

Batteries (40 batteries in all). 

One dual voltage, dual meter thyristor 

controlled charging unit. Designed 

for charging the 7AH and 22AH 

batteries simultaneously. Input voltage 

can be adjusted between 100 and 250V a.c. Built to Hiniitry 

specification. Ideal power supply For field work. Offered at 

fraction of makers' price. Two sets of batteries, 1 charging 

unit. The set £45. P. & P. 30'-. ^^ ^_ ^_ ^ — 

SOLID STATE INTERVAL TIMER " 

24-30V D.C. operation. Stabilised unijunction 

Timer and S.C.R. ' (10V I amp.), encapsulated 

in metal core. Timing interval adjustable 

from a fraction of a second to several mimites 

by means of external resistor or pot. By adding a 14V 

Relay many other complex timing Functions are possible. 

Price: 16/6 incl, circuit; P. & P. 2/6. Suitable relay JO/^gostpaii . 





MOTOROLA MAC 1 1/6 PLASTIC 
TRIAC 400 PIV. 8 AMP 

Now available EX STOCK. Supplied with full data 
and applications sheet. Price 21/- plus 1/6 P. & P. 



RE-CHARGEABLE 

BUTTON CELLS 2 x i 2v. 250 ma/hr 

Nickel Cad. Cells, connected to give2'4V @ 25 
mtliiamp/ 10 hour rate, complete with 20Q.'250V 
A.C. charger. Fully tested and unused. Price 
9/6 each plus 1/6 P. Si P. or 2 units for £1 post 
paid. 

irVsULATED TERMINALS" 

Available in red, white. yeHow, black, blue 
and green. New Price 2/- each. 




SERVICE TRADING CO 



All Mail Orders— Also Callers— Ample Parking Space 
Dept. P.E. 57 BRIDGMAN ROAD, LONDON, W.4 
Phone 995 1540 SHOWROOM NOW OPEN CLOSED SATURDAY 
780 



Personal callers only 

9 LITTLE NEWPORT ST. 

LONDON, W.C.2. Tel. G£R 0574 



AUDIO CIRCUIT DESIGN 

with 

SILICON COMPLEMENTARY PAIRS 

Motorola Publication 
12/6 Postage I /- 



HOW TO USE INTEGRATED 
CIRCUIT LOGIC ELEMENTS by Jack 
W. Streater. 28/- Postage I/-. 

THE HI-FI AND TAPE RECORDER 

HANDBOOK by Gordon J. King, 40/-. 

Postage 2/6. 

INTRODUCTION TO LOGIC 

CIRCUIT THEORY by I. Aleksander. 

32/-, Postage I/-. 

TRANSISTOR IGNITION SYSTEMS 

HANDBOOK by Brice Ward. 22/6. 

Postage I/-. 

TRANSISTOR MANUAL by General 

Electric Company. 21/-. Postage 1/6. 

BASIC THEORY AND APPLICA- 
TION OF TRANSISTORS, Dept. of the 

Army Manual. 17/-. Postage 1/6. 
SERVICING WITH THE OSCILLO- 
SCOPE by Gordon J. King. 26/-. Postage 
I/-. 

TRANSISTOR POCKET BOOK by 
R. G. Hlbberd. 25/-. Postage If-. 



I 



THE MODERN BOOK GO. 

BRITAIN'S LARGEST STOCKIST 

of British and American Tichnieat Books 

19-21 PRAED STREET 

LONDON, W.I 

Pho ne ; PA Dding ton 4 1 85 
Closed Saturday I p.m. 



4 STATION INTERCOM 




Solve your common i ca- 
tion problems with this 
4-Station Transistor Intercom system (1 master and 
3 Sub»>, In de-luxe plastic cabinets lor desk or Trail 
mounting- Call/talki'llsten Iron Master to Subs and 
Sals to Master. Ideally suitable for Business. Sut- 
gerv, Schools, Hospital . Office and Home. Operate b 
op one 9V battery. Oo/on" switch. Volume control. 
Complete with 3 connecting wires each 66It. and 
other accessories. P. & P. 7/6. 

MAINS INTERCOM 
No biltntes— no wltei. Just plug in the mains (or' 
instant two-way, inud and clear communication. 
On/oU switch and volume control with lock system. 
Price 111.18.9. P. * P. 8,'fi extra. 




Gns 

Same as ^-Station Intercom for two-way instant 
communication. Ideal as Baby Alarm and Door 
Phone. Complete with 66ft. connecting "ire. 
Battery 2/S. P. &P..4/6. . 




59/6 



'Why not boost 
business effi- 
ciency with this incredible De-Luxe Telephone; Ampli- 
fier. Take down long telephone messages or converse 
without holding the handset. A useful office aid. On/ 
off switch. Volume control. Battery 2/8 extra. P. & V. 
3/6. Pull price refunded if not satisfied In 7 days* 
WEST LONDON DIBECT SUPPLIES (PEI3) 
169 KENSINGTON HIGH STREET, LONDON, W.8 



Practical Electronics October 1970 



this can be carried out the equipment would be virtually 
useless. Most test equipment available in kit form is 
pre-calibrated or requires only simple adjustment to 
effect calibration and in any event the suppliers of kits 
usually undertake to calibrate the finished instrument 
for a nominal charge. 

Well known for test equipment kits are Daystrom 
(Heathkit) and three of their least expensive models are 
shown in the photographs. Their audio signal 
generator type AO-1U covers a frequency range of 
20 Hz to 150kHz in four ranges and provides a sine- wave 
output of up to 10 volts at less than 1 per cent distortion. 
The generator also provides a square- wave output over 
the frequency range 20 to 25,000Hz with a rise time of 
less than 3 microseconds. A fast rise time on the 
square wave output of an audio signal generator is 
essential for square wave tests on amplifiers. This 
Daystrom kit costs £14 16s Od but can be purchased 
assembled and tested for £19 18s Od. 

Also from the Daystrom range are the model OS-2 
general purpose oscilloscope and the AV-3U audio 



The Grundig MV-20 
audio millivolt meter 





The Grundig TG-10 audio 
signal generator with sine 
or square wove output 



millivolt meter both of which are suitable for a wide 
range of audio equipment tests. The 0-S2 'scope costs 
£24 18s0d as a kit, or £32 18s Od assembled and 
tested. It has a bandwidth of 2Hz to 3MHz and a 
timebase range of 20Hz to 200kHz. Other features 
are synchronisation, horizontal 50Hz sweep, a 1 volt 
reference signal and switched internal/external Y plate 
connections. 

The AV-3U audio millivolt meter has a lowest range 
of to lOmV and a highest range of to 300V. On the 
lower ranges (10 millivolts to 100 volts) the input 
impedance is 10 megohms, The intermediate ranges 
are more than sufficient for all audio work and aside 
from calibration in volts there is also a decibel scale 
directly related to the voltage readings. 



READY-TO-USE EQUIPMENT 

Many of the larger radio component stockists carry a 
wide variety of test equipment suitable for the amateur 
and at reasonably low prices. In the Nombrex range 
for instance, stocked by many dealers, there is a transis- 
torised audio generator with sine or square-wave 
output at £19 19s Od. 

There are also various Japanese made instruments of 
reasonable accuracy on the market and among these is 
an audio millivolt meter at £17 10s 0d, a sine/square 
wave audio generator at £17 and a fairly versatile 
oscilloscope with a 3 inch diameter screen at £37 10s Od. 
These are stocked by Henry's Radio Limited, 303 
Edgware Road, London, W.2., whose special test 
equipment catalogue is available free on request. 

The items mentioned above are from this catalogue 
and they have sufficient range and accurate enough 
calibration for all but precise audio tests and measure- 
ment. 

HIGH GRADE EQUIPMENT 

The greater the accuracy and versatility of test 
instruments, the more costly they become. For 
laboratory work where a high degree of accuracy is 
required there are many makes and types of instruments 
to choose from. However, the Grundig range is 
perhaps not so well known in this country as their tape 
recorders but does include an audio signal generator 
and a millivolt meter with fairly high accuracy and 
performance at a reasonably low price. 

The Grundig millivolt meter type MV-20 has a 
minimum range of 0-3mV and a maximum range of 
O-300V with 9 ranges in between. On all ranges the 
input impedance is 10 megohms and the frequency 
response is fiat from 10Hz to 1MHz. The instrument 
is also calibrated in decibels in relation to the voltage 
scales and has provision for checking its own calibra- 
tion. It retails at £55 5s Od. 

Also from the Grundig range comes their TG-20 
audio signal generator which employs a Wien bridge 
oscillator and delivers a sine or square wave output 
signal. This covers a frequency range of 10 to 1MHz 
and it has a calibrated output attenuator. The 
distortion factor is better than 0-2 per cent at the lower 
frequencies (40 to 150Hz) and better than 01 per cent 
for the remainder of the ranges. It retails at £48 1 0s Od. 

Further details of these and all other Grundig test 
instruments, most of which are high grade laboratory 
type, are available from Grundig (G.B.) Limited, 
Newlands Park, London, S.E.26. 

TAPE RECORDERS 

Grundig have just announced the release of four new 
stereo tape recorders; an automatic portable cassette 
recorder; a high fidelity three speed professional 
portable tape recorder; a new loudspeaker system 
called the "Troika" and a new systemised hi fi outfit, 
comprising a tuner amplifier, two loudspeakers and a 
transcription unit. 

The new TK3200 portable tape recorder is a half- 
track mono machine intended for professional use and 
should be up to that standard since it retails at 
£178 3s Od. The new domestic recorders cover a wide 
variety of facilities and are available for half or quarter- 
track stereo with prices ranging from £54 1 5s 7d for the 
TK21 model to £157 14s Od for the TK248. 

The TK248 is a de-luxe model with twin 8 watt 
output stages, four built-in loudspeakers and facilities 
for multi-play, signal mixing, echo and monitoring on 
or off tape. 



'Practical Electronics October 1970 



781 




Archaeologists, treasure hunters and skin divers 
have a common problem, where to dig or dive to 
discover the loot. A buried metal locator would come 
in handy, but most are either expensive or have too 
limited a range. The one described here is a proton 
magnetometer utilising discoveries made in nuclear 
magnetic resonance first published in 1946. 

Some care is required in putting together the high 
gain amplifier, but otherwise construction is straight- 
forward, using standard components, and the exotic 
nuclear material is distilled water. 

Essentially, the magnetometer measures the intensity 
of the earth's magnetic field at two nearby points. A 
difference in the intensities produces an output from 
the device, which can be either an audio signal or a 
meter reading. 

The earth's field is normally uniform, but will be 
disturbed by local concentrations of magnetic materials, 
such as iron ore or just iron junk. Hence the magneto- 
meter can only be used to search for ferrous materials or 
compounds. For this purpose it is extremely sensitive 
with considerable range. 

It will, under ideal conditions, detect a one pound 
mass of iron at about four or five feet below one of the 
bottles, and larger masses at much greater distances. 
Typical of the latter is a twelve foot length of three inch 
diameter iron water pipe at twelve feel. It is difficult 
to give performance figures, since much depends upon 
the size, density and attitude of the object disturbing the 
field, and experiment provides the best answers. 

This high sensitivity to field variations means that the 
magnetometer may only be used remote from known 
earth field disturbers, such as buildings and power 
lines. 



ATOMIC PRINCIPLES 

To understand the principles involved is easy, if the 
cobwebs and dust are shaken off the school books and 
memories of atomic particles. Remember that old 
friend, the hydrogen atom, first in the atomic table, 



with just one proton and one orbiting electron, as 
simple a thing as any alchemist could wish. 

The orbiting electron acts just like electric current in 
a coil of wire and sets up a magnetic field about the 
atom as seen in Fig. 1. The proton, the main mass of 
the atom, is also in motion, spinning about its centre, so 
that the whole atom looks like a magnetic gyroscope, 
whose magnetic poles are on its spin axis. 

Gyroscopes have idiosyncracies revealed to 
mechanical engineers, one of them being that they will 
precess if acted upon by an external field. In the 
hydrogen proton's case, its spin axis will wobble or 
precess about the direction of the earth's magnetic field, 
if that is the only magnetic field acting on it. This is 
shown in Fig. 2. The frequency of precession will be 
proportional to the strength of the field and is given by 
v = kB where v =•■ frequency of precession 

k = 4-26 x 10 3 Hz/weber for 
hydrogen 

B = intensity of magnetic field. 

USE OF DISTILLED WATER 

If a coil of wire is wound round a small plastic bottle 
containing distilled water, sufficient current can be 
passed through the coil to set up a local field in the 
bottle very much greater than any external field, in this 
case the earth's. 

A number of the spinning protons of the hydrogen 
atoms, remember H a O, happily line themselves up with 
their spin axes along the direction of the induced field. 
If the current is suddenly cut off, the induced field 
collapses, and the protons try to realign themselves with 
the earth's field. 

Because they behave as gyroscopes, they cannot 
simply switch back, but must precess back at the pre- 
cessional frequency. In doing so they set up a very 
weak alternating field in the bottle, and an alternating 
voltage is induced in the coil. This voltage falls to 
zero as realignment with the earth's field is completed. 
Fig. 3 shows the signal that would be seen on an 
oscilloscope. 



782 



Practical Electronics October 1970 






A combination of nucleonics and electronics provide an extremely 
sensitive detector with long range search capability. Detection principle 
is based on local variation in earth's magnetic field. 



by L. HUGGARD, b 



.Sc. 




~JS 




FERROUS METAL LOCATOR 




PRECESSION 



Fig. I, Magnetic field 
around hydrogen proton 
produced by orbiting 
electron 




fig. 2 Precession of proton 
relative to earth's field when 
acted upon by external 
magnetic influence 




Fig. 3. Diminishing alternating voltage set up by preces- 
sion frequencies from the detector coils 



EARTHS 



Modulation kiwI up* 




BASIC MAGNETOMETER 

This phenomena can now be used to make a ferrous 
metal detector. Two such bottles filled with distilled 
water are spaced about six feet apart. The longitudinal 
axes of the bottles He east-west. 

The coils wound round the bottles are connected in 
series and a current passed through them. After three 
seconds, the current is cut off and an amplifier con- 
nected across the coils. If the intensity of the earth's 
field is the same at each bottle, the precession frequency 
at each will be the same, and the signals from both coils 
of equal frequency. 

If, on the other hand, the field intensities weredifferent 
due to some local magnetic disturbance, then the signal 
frequencies will differ, and the difference can be 
detected. 

The amplifier input signal is then the sum of two 
signals of slightly different frequencies and its output 
will be a signal of a third frequency which is half the 
sum of the two input frequencies. The amplitude of 
this is modulated at a fourth frequency equal to the 
difference between the original two input frequencies. 
This composite output signal can be heard in a headset 
as a note of about 2kHz with a marked quaver. This 
is illustrated in Fig. 4. 



IRON MASS CAUSING LOCAL 
INCREASE IN FIELD INTENSITY 



Fig. 4. Modulated output produced by mixing the two 
precession frequencies from the detector coils 

Practical Electronics October 1970 







783 



DETECTOR BOTTLES 
(Fi<|l5) 




Fig. 5. Block diagram of proton magnetometer 



The greater the difference in the field intensities 
between the two bottles, the faster will be the quaver. 
It only remains to reach for the shovel and see what is 
causing the magnetic difference. 

CIRCUIT BLOCKS 

Now look at the block schematic of the magneto- 
meter in Fig. 5. There are in effect six units comprising : 
two detector bottles, relay circuit, multivibrator, main 
amplifier, meter amplifier, and power supply. These 
form what might be called a de-luxe unit. The relay 
and meter circuits may be omitted if costs have to be 
kept down. 

The relay is used to switch the series wound coils, LI, 
L2 from the "polarise" condition to "detect". In the 
"polarise" condition the relay passes current through 
the coils via terminal BI at the stabiliser. On "detect" 
the relay switches the precession frequencies produced 
at the coils to the main amplifier input terminals Al, 
A2. Detection of the modulation envelope is then 
provided for, both aurally and visually, by the head- 
phones XI and meter Ml. 

The relay can be , made to operate manually by the 
push-switch SI or automatically when coupled via S2 
to the multivibrator; this switch does in fact select the 
mode. 

The multivibrator switches the relay on for about 
three seconds and off for the same period. This 
continuous operation is particularly useful when 
searching. The manual option is used when setting up 
or detecting a very small frequency difference. 

RELAY DRIVER AND MULTIVIBRATOR 

The circuit diagram of the relay driver and multi- 
vibrator is given in Fig. 6. Here TR1 and TR2, in 
modified super alpha configuration, drive the relay. 



784 



The relay contacts are shown in the quiescent state. 
A 1W resistor, Rl, can be inserted in the "polarise" 
circuit to reduce the detector coil current and so cut 
down on battery consumption. It follows that the 
higher the value of this resistance the smaller will be the 
signal presented to the main amplifier, so the choice of 
value should be made when the unit is completed and 
tested; 4-7 ohms is a suitable value to start with. "Cut 
and try" methods should provide balance between a 
tolerable signal and battery economy. 

The multivibrator, comprising TR3 and TR4, 
provides an equal mark-space output of three seconds 
duration at the collector of TR3. This is passed via S2, 
when switched to the "auto" mode, to the base of TR2. 

Details for assembling and wiring this circuit module 
are given in Fig. 7. 

Relay driver and multivibrator board 



%HW^ 




/ Practical Electronics October 1970 



DETECTOR BOTTLES 



RELAY DRIVER 



DETECT 
^POLARISE' 



MULTIVIBRATOR 



r~ 



rn./5 

I I 

LJ- 




PL1 



RLA1 



LI 
0-O21H 



/ F PU 



PL3 



m 



I I 




0-021H 



£z^r® ®^ 



PL4 



^ 



Fig. 6. Circuit diagram of relay driver 
and multivibrator 



Fig. 7 (below). Assembly and wiring 
details of relay driver and multivibrator 
board 





COMPONENTS 



RELAY DRIVER AND MULTIVIBRATOR 
Resistors 



Rl' ; 

R2 

R3 

R4 

R5 



See text 
Ikfi 
Iktt 
82k n 
33k £1 



R6 
R7 
R8 
R9 
RIO 



[OkQ 
330k Q 
330k Q 

I Oku 

ison 



All £W, 10% carbon except where otherwise stated. 



Capacitors 

CI lOO^F elect. 25V 
C2 5 M F elect. 25V 
C3 5,uF elect. 25V 



Transistors 

TR| 2N26I3 
TR2 2N5088 
TR3, TR4 2N27I2 

Diodes 

D I OA202 



(2 off) 



Switches 

51 Press switch 

52 Single-pole changeover 

Relay 

RLA 12V I85Q 4 pole-changeover 

STC miniature relay type 25 (Electroniques) 

Miscellaneous 

Veroboard 4in 



2£in, 0-15 

SKI-SK4 phono sockets (4 off) 



ma^ix plain, 



Practical Electronics October 1970 



785 



^.--ZZZIZ Otl 




Fig. 8. Circuit diagram of main amplifier 



MAIN AMPLIFIER 

The main amplifier, seen in Fig. 8, serves lo increase 
the level of the precession voltages. A ferrite cored 
transformer, Tl, with the 'primary centre tapped, is 
tuned to the required frequency by C4 and C5. The 
first stage comprising TR5 has a tuned collector load 
resonant at the same precession frequency. 

The output from the secondary of T2 feeds the d.c. 
coupled amplifier TR6-TR7, This acts, in effect, as a 
pre-amplifier to the meter circuit, the input for this 
being taken from Ml. 

The bandwidth of the tuned circuits is about 300Hz, 
which has proved adequate on field trials. 

VR1 is the volume control for the headphone 
amplifier, TR8-TR9, the output being taken via. JK1. 

The headphones used should preferably be high 
impedance crystal, since magnetic ones can cause 
feedback trouble if brought too close to the detector 
bottles and so cause the amplifier to oscillate. 



(In field trials magnetic phones were used and proved 
trouble-free provided they were maintained in the plane 
of the detector bottles.) 

AMPLIFIER CONSTRUCTION 

Since the amplifier provides high gain, the wiring 
layout and constructional details of Fig. 9 should be 
adhered to, to prevent instability. 

Both of the transformers are contained in Vinkor 
adjustable pot cores. To wind Tl use 40 s.w.g. enamel 
covered wire. Slip a couple of inches of fine sleeving 
over the start to protect the leadout, then wind on seven 
hundred and fifty turns. Put on another piece of 
sleeving over the finish leadout and wrap a layer of 
cellotape round the winding. 

Put on two more windings of three hundred and 
seventy-five turns each and identify the starts and 
finishes with different coloured sleeving. Wind a layer 
or two of plastic electrical tape around the completed 




Alain amplifier board 



786 



Practical Electronics October 1970 




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788 



Practical Electronics October 1970 




Fig. 9. Assembly and wiring layout of main amplifier board 



COMPONENTS 



Resistors 

Rll 39k Q 



MAIN AMPLIFIER 



RI2 
RI3 
RI4 
RI5 
RI6 
RI7 
RI8 
RI9 
R20 
All i 



33 k Q 

I Ok metal oxide 

2-2kQ 



stated. 

Capacitors 

C4 0-lfiF 



15k a 

18k a 
22 D 
47k O 
4-7kfi 
4-7kQ 
watt, 10% carbon except where otherwise 



R2I 
R22 
R23 
R24 
R25 
R26 
R27 
R28 
R29 



68k Q 
820D 
4-7k£2 

1 2k a 
iood 
12k a 

2-2kQ 
I -2k a 
iok n 



CI4 5^F 
CIS 25/^F 
CI6 I0 M F 



elect, 
elect, 
elect. 



6V 
6V 
15V 



Transistors 

TR5-TR9 2N5088 (5 off) 

Transformers 

TI-T2 LA230I 



10% 

"0% 

6V 

15V 

6V 



polyester 

C5 0-0'22 M F polyester 

C6 SftF elect. 

C7 30^F elect. 

C8 25/iF elect. 

C9 8,200pF polystyrene 10% 

CIO 5 M F elect. 6V 

CI I 100/xF elect. 15V 

CI2 SOfiF elect. 15V 

CI3 5/iF elect. 15V 



pot cores — Type "B" Assembly 
consisting of adjuster, clip, cup core, 
bobbin and tag board. (Gurney's Radio, 
91 The Broadway, Southall, Middlesex) 
(2 off) 
(see text) 

Potentiometers 

VRI 20k Q linear 

Socket 

JKI Standard jack socket 

Miscellaneous 

Veroboard 6±in x 2fin, OlSirt matrix, plain 40 
s.w.g. wire 



windings then very carefully assemble the bobbin in 
the ferrite core. Ensure that nothing gets trapped 
between the two halves of the core, preventing them 
mating. 

If test equipment is at hand, the inductance of the 
seven hundred and fifty turn winding should be 
0196H, and its resistance about 56 ohms. The resis- 
tance of each of 'the other windings will be 28 ohms. 

COUPLING TRANSFORMER 

The coupling transformer T2 is built in the same way. 
Its primary winding has 1,076 turns of 40 s.w.g. and the 
secondary 258 turns of 40 s.w.g. When finished the 
primary inductance should be 0-4H and its resistance 
about 88 ohms. The secondary resistance will be about 
26 ohms. 

Since final tuning of the amplifier is made during field 
trials, the capacitors C4, C5 and C9 should be 
temporarily connected using crocodile clips. 




Meter amplifier board 



Practical Electronics October 1970 



789 




Fig, It, Assembly and wiring layout of main amplifier 
board 



COMPONENTS 



METER AMPLIFIER 
Resistors 

R30 56k n 
R3I 33k Q 
R32 56k Q 
AII±W, 10% carbon 

Capacitors 

CI7 5 M F elect. 15V 

CI8 00I2^F 5% polystyrene 

CI9 l(VF 6V 

C20 l M F 15V 

Potentiometer 
VR2 20k fi linear 

Transistors 

TRIO 2N5088 
TRII 2N404 

Diodes 

D2, D3 0A202 (2 off) 

Inductor 

L3 0-4H LA230I pot core— Type "B" Assembly 
(See text) 

Meter 

Ml 0-lmA moving coil 2|in square 



ft 1!« Scrttn kads 
from SKJ-5K4 

. Fig. 13. Assembly and wiring layout of the stabiliser board 

COMPONENTS . . . 



STABILISER 

R33 lOOfl R34 270 Q R35 I50Q 

All £W, IO D carbon 

Capacitors 

C2I 500^ F elect. 15V 
C22 500^F elect. 15V 

Diodes 

D4 ZL24 9- IV I-5VY Zener 
D5 IS401 

Switch 

S3 Single pole on/off 

Lamp 

LP I 6V 006A MES bulb to fit 
Eagle IL. 1 15 Indicator Lens (G. W. Smith Ltd) 

Fuse 

FSI 2A fuse and holder 

Sockets 

SK5, SK6 4mm insulated terminals coloured red 
and black (2 off) 



790 



Practical Electronics October 1970 




*mpfffl*r lovt 



HuRinbrtior torn 



METER AMPLIFIER 

The circuit for the meter amplifier is given in Fig. 10. 
Here VR2 acts as a sensitivity control in feeding the 
complementary pair TRIO and TR1 1. 

The meter circuit can be used in conjunction with, or 
to replace the headset. 

The meter needle follows the amplitude of the 
amplifier output which varies at a rate equal to the 
difference between the two input frequencies. It is 
particularly useful with very low difference frequencies. 

Constructional details of this module are given in 
Fig. 11. 

The inductor' L3 is contained in an adjustable pot 
core, the type being the LA2301, the same as used in 
the main amplifier. 

To achieve the specified inductance, 1,076 turns of 
40 s.w.g. enamel covered wire should be wound on the 
bobbin. With the winding complete the free ends 
should be cleaned and the bobbin assembled in the cup 
cores. 

The mating surfaces of the cores should be fixed 
together with an adhesive such as Araldite. and the 
whole stuck to the Vero board. 

POWER SUPPLY 

The power supply stabiliser circuit is shown in Fig. 12. 
Here the diode D5 will prevent damage if incorrect 
connection to the power source is made. 

The supply to the main amplifier and multivibrator is 
taken from the Zener diode D4, and that for the meter 
circuit is additionally decoupled by R33 and C21. 

Three separate chassis connections, G1-G3, are made 
between the main amplifier and stabiliser to prevent the 
possibility of oscillation. 

The supply lead from the 12V battery must be 
screened. The centre wire is positive and terminates at 
SK.5; the negative screen at SK6. Constructional 
details are. given in Fig. 13. 

Since the magnetometer draws about 750mA during 
"polarise", an adequate heavy duty power source must 
be used. 



Fig. 14. Control panel wiring to boards 



CHASSIS ASSEMBLY 

Assembly details of the modules on the chassis and 
front panel interwiring is given in Fig, 14. It should 
be emphasised that the chassis must be aluminium, and 
contain as few iron parts as possible, ideally none. 

DETECTOR BOTTLES 

The detector bottles are plastic, lfin outside diameter 
and 4in long. The bottle caps must be plastic. 

COIL FORMERS 

The coil formers for the bottles are made to be a 
sliding fit. One way to do this is to roll each bottle in 
a couple of thicknesses of paper, cover that with a layer 
of thin plastic sheet, such as is used for food wrapping, 
and then wind on two or three layers of glass cloth as 
shown in Fig. 15. 

The glass cloth is impregnated with epoxy resin and 
left to cure. The final thickness of the former wall 




Prototype power supply stabiliser board 



Practical Electronics October 1970 



791 



Fibre glass tube 




Foam 

Rubber 

sheath 

Plastic bottle filled bubble 
free with distilled water slides 
Winding into fib re gl ass tub* . 



Gail Cheeks 3 diaXft 
thick wood at each 
end 



Fig. 15. Constructional details of detector coil former 

COMPOHENTS . . . 



Detector Coils 

LI, L2 0021 H 750 turns of 24 s.w.g. enamelled 
copper wire wound on I fin x 4in plastic 
bottle formers (2 off) (See text) 

PLI-PL4 Phono plugs (4 off) 

Carrying staff 

4-in wood cut as required 4-^in brass wood screws 
(see text) 

All Other Miscellaneous Items 

Aluminium chassis and top panel 13iin X Sin X 24in 
(H. L. Smith) 

Knobs (2 off), carrying strap, plastic covered con- 
necting wire, twin conductor screened lead, 
single conductor screened lead. 

BYI — 12V, HPI 



z3/< life 



sv: 



M' 



V 



5/1 






VjbnqXKoB C&nkhead 
brass wood screws 



i f""" ^ii: 



">7 



Bottles secured to battens 
with rubber bands 



l'/8 

_t_ 



L, J 



Material: ^ Chick wood 
througout 



Fig. 16. Constructional details of carrying staff 
792 



should be about &in. Once the epoxy has hardened, 
the outer surfaces should be sanded smooth, and two 
wooden cheek pieces epoxied on. This gives a very 
rugged former. Two small holes are drilled in one 
cheek, one close to the bottom, the other near the top, 
to bring the ends of the coil out through. The former 
is then covered with a layer of insulating tape. 

WINDING THE DETECTOR COILS 

Carefully solder an eight inch length of fine plastic 
covered multistrand wire to the start of the coil wire and 
insulate the joint with thin sleeving. 

Three inches of the. multistrand wire are passed out 
through the bottom hole in the cheek to make the 
wiring connections to. Seven hundred and fifty turns 
of 24 s.w.g. enamelled coil wire are now wound on. 
The winding should be as neat and even as possible. 

If a lot of rough use is foreseen in the future, it might 
be prudent to spend a little more and use coil wire with 
a tougher coating. A suitable coating is armoured 
polythermaleze. With the winding completed the free 
end is joined to another piece of multistrand, the joint 
insulated and the wire taken out through the remaining 
hole in the cheek. 

The complete winding is covered with a couple of 
layers of plastic insulating tape. For further protection, 
put on a layer of thin foam rubber or plastic. At this 
point take a break to steady the hands and then make 
the second coil in exactly the same way. 

Now if it is possible to measure the coils, the induct- 
ance of each should be 0-021 H and the resistance about 
7-9 ohms. 

CARRYING STAFF 

Details of the carrying staff construction are given in 
Fig. 16. This is of wood, the cross members being 
attached with brass wood screws. 

D.C. CHECK OUT 

Give the wiring and all solder joints a final careful 
check, making sure that all semiconductors are con- 
nected correctly. Set all controls to minimum and 
connect to a 12V power source. Switch on and check 
all given d.c. voltages with a test meter (20,000 ohms 
per volt). 

Operate the press switch SI which should energise 
the relay when the switch S2 is at "Manual". Switch 
the latter to "Auto" ; the relay should now cycle on for 
three seconds and off for three seconds. 

If the periods are unequal try substituting different 
electro] y tics for either C2 or C3 in the multivibrator. 
These capacitors have a very wide manufacturing 
tolerance which may affect the timing. Once the meter 
circuit is cycling correctly, connect the test meter across 
the detector input sockets SKI and SK4. The meter 
should read 12V when the relay is closed, and zero 
volts when it is open. Switch the supply off. 

Check that the meter reads about 43 ohms across the 
input sockets SKI and SK3. This ensures that the 
relay is switching the two inputs to the input trans- 
former. 

METER AND FIELD CHECK 

Connect up the detector bottles and turn the supply 
on again. 

If an oscillator is available, make a loop of wire across 
its outputs and set it near the end of one of the bottles. 

Turn up the amplifier gain control slightly and a loud 
note should be heard in the headsets if the oscillator is 
adjusted between 2,000Hz and 2,500Hz. At this 

Practical Electronics October 1970 



BATTEN OH STAFF 



i4> 



L. 



"~l 




SEARCH PATH 



DISTANCE APART OF SEARCH PATHS 
DETERMSNED BY EXPECTED DEPTH 
AND SIZE OF OBJECT BEING SOUGHT 



Place a pound mass of iron — pair of pliers or 
hammer — about two feet below one of the bottles and 
switch S2 to "Auto". 

QUAVERING NOTE 

A note with a marked quaver should be heard on the 
"detect" portion of the relay cycle. Adjust the gain to 
give a convenient output in the headset. 

Vary the distance between the iron mass and the 
bottle until the note peaks about five times during 
"detect". 

Try going up or down a few preferred values on the 
tuning capacitors to get the loudest signal. Then fine 
tune by adjusting the tuning core in the ferrite cores. 
If the gain of the meter circuit is turned up the meter 
should follow the amplitude of the detected signal, the 
height of the peaks shown falling over the detect period. 

All is now in order, heave a sigh of relief, the 
magnetometer is ready to go to work. 

USING THE MAGETOMETER 

It is probably obvious by now how the device can be 
used. The area to be searched should be traversed, 



Fig. 17. Search pattern that 
should be followed when using 
the magnetometer 



Fig. 18. Arrangement of 
magnetometer equipment in 
a boat 




frequency turn up the meter gain control until the meter 
reads about half scale. Turn the oscillator off, where- 
upon the note should disappear, and the meter needle 
fall to zero. 

Switch S2 to "Auto", the coils will now be energised 
each time the relay is closed. This can be checked by 
holding a compass near each one and seeing that a field 
is produced. 

No further testing can be carried out indoors. The 
unit must be taken to some spot at least a quarter of 
a mile from all wires, buildings, and possible sources of 
electrical or magnetic interference and ferrous junk. 

TUNING 

The resonant circuits have now to be tuned to the 
exact precession frequency produced by the earth's field 
at the site chosen for the test. This will be between 
2kHz and 2- 5kHz. 

Once so tuned the magnetometer can be used within 
a radius of a hundred miles or so of the test site. At 
greater distances the tuning should be checked, and 
corrected if necessary. 

The staff with the bottles should be set with the bottle 
axes pointing east-west, that is the staff points north- 
south (see Fig. 4). The chassis should be somewhere 
along a line east-west through the middle of the staff. 

With S2 switched to "Manual", turn the audio gain 
full up. There should only be some noise in the head- 
set, and no trace of oscillation. Now turn the gain 
down to about half. 



moving so that the coil axes point east-west; this 
gives maximum sensitivity. 

Move fairly slowly, remember that it takes six seconds 
for one polarise and detect cycle, so do not overshoot 
small objects. 

Alternatively, walk a couple of steps, let the device 
cycle and then move on a few more. Once something is 
detected, move around until the quaver reaches its 
fastest, when the "something" should be somewhere 
beneath. 



DETECTION CAPABILITY 

The size of that something and how far down it is 
will only be resolved by digging. As a rough and ready 
guide as to what to expect, a one pound mass should be 
detectable at about five feet below one of the bottles, 
and a one ton mass at around forty feet. 

Size, distribution of metal and the attitude of the 
object all affect the magnetometer's ability to detect it; 
the best way to evaluate its performance is by experiment 
with a number of different objects. 

In Fig. 17 is shown the traverse pattern that should be 
employed for overland searches. 

When working from a boat it is simpler to keep the 
bottles near the surface, rather than make an elabor- 
ate underwater housing to get it near the bottom. Using 
this method, some idea of a wreck size and depth can 
be more easily estimated. A typical arrangement for 
aquatic search purposes is given in Fig. 18. -fa 



Practical Electronics October 1970 



793 



THERMISTOR 
THERMOMETER 

A SPECIAL PROJECT FOR BEGINNERS 



This month we present an Air Thermometer with a 
range of 0-50°C (32-122°F) which is more than 
adequate for indoor measurement. Since the readout 
is essentially a linear function of temperature, a sensitive 
50/tA moving coil meter can be used directly, no scale 
re-calibration being necessary. 

THERMISTOR BRIDGE 

The element of the circuit in Fig. 1 which makes 
temperature measurement possible is the thermistor XI. 
Unlike ordinary conductors its resistance decreases with 
increasing temperature. In order to magnify the effect 
of the current variations produced, the thermistor has 
been arranged with other resistors and potentiometers 
to form a bridge circuit and so multiply the effects of 
thermal changes at the meter. 

To understand the working of the bridge let SI be 
switched to the temperature measurement position. 
Looking round the bridge arms it can be seen that the 
lower arms are of equal resistance with variation 
possible at the upper arms in VR1 and the thermistor. 

To arrange that zero current through the meter 
coincides with an environmental temperature at 
the thermistor of 0°C means adjusting VR1 until the 
voltages across R3 and the meter Ml are equal. The 
bridge is then said to be balanced. 

When the thermistor subsequently is exposed to other 
higher temperatures in the range 0-50 c C its resistance 
changes proportionally to the new temperature and the 
bridge is unbalanced. The voltage across R3 and Ml, 
is then proportional to the temperature change. 

LINEAR TRACKING 

In order to linearise the thermistor's logarithmic 
resistance/temperature characteristic it is necessary to 
add the resistors R5 and R6. Since manufacturing 
spreads can provide variations of ±20 per cent on 
this characteristic it may be necessary, in individual 



cases, to vary slightly by experiment, the value of those 
resistors for linear tracking of the meter with tempera- 
ture change. 

CONSTRUCTION 

The T-Dec is used for mounting the majority of small 
components, the pre-set potentiometers being connected 
to the control panel. Assembly details are shown in 
the photograph. 

Be careful when soldering the thermistor leads to wire 
lengths as the former are fragile, in addition they 
should not be reduced in length. When joints are made 
they should be sleeved to prevent inadvertent short 
circuits. 

Since there is nothing critical in the circuit apart from 
the calibrations, other constructional methods may be 
employed. 

CALIBRATION 

The requirements for calibration are an ordinary 
Celsius mercury thermometer and environments for 
fixing the scale limits. Since the stabilisation of the 
zero point (0°C) takes some time a refrigerator freezer 
compartment is to be preferred in fixing this lower 
reference. 

With the potentiometer VR3 set to about mid- 
position and the thermistor placed in the freezer, adjust 
VR1 for a null on the meter. This adjustment should 
be maintained over a period of ten minutes. 

To fix the upper point (50° C), the thermistor should 
be transferred to a water bath heated to this tempera- 
ture. Since the thermistor lead is glass encapsulated 
this can be partially immersed, but make sure the wire 
leads do not come in contact with the water. 

To obviate inaccuracies, the water should be stirred 
from time to time with the bulb thermometer. When 
this indicates 50°C adjust VR3 so that the meter needle 
aligns at 50/iA. The calibration procedure should be 
repeated at least twice. 







794 




Practical Electronics October 1970 



J0*" 



"Jjfr^ ^^^ 





Fig. I, Circuit diagram 
of the air thermometer 



The meter should be checked for tracking linearity by 
reducing the temperature of the water bath. If iced 
water is added this part of the calibration can be 
rapidly undertaken. Once again before each measure- 
ment the water should be stirred and comparisons 
between meter and bulb thermometer made at 10 degree 
intervals. 

If the readings are graphed, temperature against 
microamps, the plots made should roughly align with a 
straight edge; if not the value of R5 and R6 may need to 
be slightly altered. Here, R5 will affect the lower end 
of the meter scale and R6 the upper. Experiment with 
resistor values approximating to those given should 
provide linear tracking. 




36 A 



BATTERY CHECK 

With deterioration of the battery and consequent 
reduced line voltage, meter readings will be displaced 
from true so it is necessary to compensate for this. 

In the initial calibration it was arranged that the peak 
temperature reading should coincide with the 50 mark 
on the meter. If a potentiometer is arranged to have 
the same total resistance as that contained in the 
thermistor arm at that temperature then it can be 
switched in when required as an upper point calibration 
check. 

VR2 is adjusted to achieve this; when it is necessary 
to check the battery condition SI is switched to 
'"calibrate". If the meter needle shows full scale 
deflection, all is well; if not, VR3 should be adjusted. 



R5 6 8kil 
R6 3?0n 



COMPONENTS . . . 

Resistors 

Rl I'SkO R3 5-6kQ 

R2 f-5kft R4 l-5kf2 

All 10%, ± watt carbon 

Thermistor 
XI THBI2(Radiospares) 



Potentiometers 

VRI 5kQ VR2 2kSl VR3 500O 

All wirewound linear presets 

Meter 

Ml Moving coil meter, 0-SQ^A f.s.d. 

Switch 
SI Single-pole, 

double-throw toggle switch 



Battery 

BY I 4 volt, HP2 

Miscellaneous 

T-Dec, connecting wire 




Practical Electronics October 1970 



795 



This concluding article in the series continues with 
■ electromechanical output transducers, particle and 
radiation sensors, then follows with special purpose 
Semiconductor devices. 



CONCLUSION OF 
A NEW 
SERIES FOR 
THE BEGINNER 




The servo uses a dx. motor as an output transducer, 
which is coupled via a gearbox to a feedback potentio- 
meter. As the diagram in Fig. 7.1c shows, a pinion 
gear on the gearbox shaft can convert the rotational 
motion of the motor spindle into a linear push-pull 
movement when so required. 

The d.c. servo operates as follows. In the absence 
of an input signal the motor is stationary with zero 
volts at the amplifier output, and the potentiometer 
slider is half way along the resistance track. When a 
d.c. signal is applied to the comparator, it will be 
amplified to a level sufficient to cause the motor to 
rotate. 

The potentiometer slider moves to a setting where the 
feedback signal has the same value as the input signal 
and is of opposite polarity, thus cancelling the input 
signal and switching the motor off. 

Stepping Motor 

Stepping motors are derived from synchronous 
motors of the type used in clock and timer mechanisms. 

When connected to a special electronic switch circuit, 
the stepping motor can be speed-controlled in both 
directions, and will also offer a rotational output 
consisting of a series of angular steps. The- stepping 
motor armature has permanent magnet poles — usually 
12 — and two field coils, see Fig. 7. Id. 

If a single pulse is fed to one of the inputs of the 
electronic switch the armature will move A of a 
revolution, but a fast train of pulses at the input will 




ELECTROMECHANICAL OUTPUT 
TRANSDUCERS 

We are concerned here with devices that provide a 
mechanical force to push, pull, rotate, or accurately 
position some mechanical system in response to an 
electrical signal. 

Solenoid 

The solenoid in Fig. 7.1a is a straightforward example 
of a mechanical output transducer for pushing or 
pulling. A cylindrical plunger of ferrous material is 
drawn into the coil by the magnetic field arising from a 
current flowing in the wire turns. The force is only 
attractive and the plunger is returned to its original 
position by a spring when the current ceases to flow. 

Electromagnet 

Another simple type of transducer for supplying a 
mechanical force is the electromagnet with pivoted 
armature as in Fig. 7.1b. When a current flows 
through the coil, the core is magnetised and attracts 
the ferrous armature against the tension of a return 
spring. 

Ser vomeckanisms 

A more sophisticated arrangement for accurate linear 
or rotational positioning is the d.c. proportional servo, 
so called because the output motion is proportional to 
the input signal. Applications include the remote 
panning of closed-circuit television cameras, rotating 
aerials, and radio control of models. 



cause smooth rotation at a rate dependent on pulse 
repetition frequency. Thus, there can be complete 
control of motor speed and spindle positioning. 

PARTICLE AND RADIATION SENSORS 

Radioactive substances emit electromagnetic waves 
(gamma rays) and high speed atomic particles. Gamma 
radiation is equivalent to x-rays of high energy. There 
are several kinds of particle, such as the fast moving 
electron (beta particle) and the helium nucleus (alpha 
particle). 

Silicon Alpha Detector 

Alpha particles can be counted by specially con- 
structed silicon diodes, and germanium diodes — with an 
extra layer of intrinsic semiconductor material inserted 
between the n- and />-type regions (pin diode)— will 
respond to gamma rays. 

The silicon diode in Fig. 7.2a has a gold leaf window 
which offers little resistance to the passage of an alpha 
particle. When reverse biased, the diode emits a pulse 
as an alpha particle penetrates the window and causes 
ionisation of silicon atoms. 

Geiger-Miiller Tube 

The Geiger-Miiller tube (Fig. 7.2b) is an extremely 
sensitive detector of individual beta particles and 
gamma ray quanta. The tube is filled with an inert 
gas plus additives to ensure that an electrical discharge 
between the cylindrical and wire electrodes is quenched 
quickly. 



796 



Practical Electronics October 1970 



i«!i!i!!!!ELECTROMECHANICAL OUTPUT TRANSDUCERS iiiiiiiiiii 



REFERENCE 
f VOLTAGE 1 



AiVVV 

| POTENTK>Mt 
-*— fEEIMACK | 




INPUT 
«V" ° yy | AMPLIFIER 

comparator 





Fig. 7.1a. Moving core solenoid 

Mr 



>f^*^^ PROWMTIOKAl 
LINEM NOTION 

Fig. 7.1 e. Proportional d.c. servo mechanism 



»» 



POTENTIOMETER ■■ 

/ ■■■■ 

1 



■ ■■■ 

■■■■ 

■ ■*• 

■ ■*■ 




PULSE INPUT FOR 

ANT I- CLOCKWISE ROTATION 

am 





_frain 




BAR MASNETS ON AtttATUtE 



Fig. 7.1b. Electromagnet relay switch 



Fig. 7.1 d. Synchronous stepping motor (magslip) 



■■■■ 

field :::: 

YMOtNCS ■■■* 



pi** 

■ ■■■ 

■ ■■• 

■ ■■■ 



WAY TO ELECTRONICS 



RADIATION SENSORS 



PHOSPHOR 
CRYSTAL 




J 



+-400V 




PHOTO MULTIPLIER TUBE 



(J^ilh 



*h 



DYNODES ANODE 



CATHODE 



rn^l 





output ::■- 



Fig, 7.2a. Silicon alpha 
particle detector 



Fig. 7.2b. Geiger-MUIter tube 



Fig. 7.2c. Scintillation counter 



Practical Electronics October 1970 



797 



■ ■■■«■!■■*■ ■■*■■:*■■ ft ■■tall ft ■■■■■■■*.■■■■■*■>■■■«■■■«■■■ 



HOT FILAMENT 
ELECTRON SOURCE 



TARGET MATERIAL 




Fig. 7.3a. Linear particle accelerator 



HOT FILAMENT 
(CATHODE) 



TUNGSTEN TARGET 
(ANODE) 




X-RAY5 
Fig. 7.3b. X~ray tubs 



+100 KV 



On arrival of a particle, a momentary discharge takes 
place, due to ionisation of gas atoms, thus giving an 
output pulse. The tube is ready to receive the next 
particle after a recuperation period of about 200 micro- 
seconds. 

Scintillation Counter 

Certain transparent materials and crystals will emit 
flashes of light when bombarded by nuclear particles. 
In the scintillation counter, a photomultiplier tube is 
employed to detect each flash. 

Briefly, the process is as follows, see Fig. 7.2c. A 
minute flash of light within the transparent block of 
material is picked up by the photomultiplier cathode, 
which then ejects a few electrons. The electrons then 
travel to the. first dynode and liberate more electrons. 
So, at each dynode there is a progressive multiplication 
of the electron stream, leading to a large electrical 
output pulse when the electrons finally arrive at the 
anode. 

Particle Accelerator 

The linear accelerator in Fig. 7.3a emits a beam of 
high speed electrons having the same properties as beta 
particles from a radioactive substance. 

Electrons from a hot filament source are accelerated 
along the tube by an alternating, high frequency field 
applied to cylindrical electrodes. The electrons are 
given a "kick" by the high frequency field at each gap 
between adjacent electrodes, thus gaining velocity and 
resulting in a high energy beam. This beam can either 
be used to bombard a target or may be emitted from the 
tube via a thin window. 

X-Ray Tube 

An x-ray tube is shown in Fig. 7.3b. A hot filament 
cathode provides a source of electrons, which are 
accelerated towards the anode by a large positive 
potential. When the electrons strike the anode target, 
about one per cent of their energy is converted into 
x-rays, the remainder is given off as heat. The x-rays 
emerge from the tube in a conical beam. 



THE SEMICONDUCTOR FAMILY 

Transistors and semiconductor diodes are important 
members of a growing family of devices, all depending 
on the special properties of pn junctions. Some of 
these associated devices will now be examined. 

FIELD EFFECT TRANSISTORS 

A conventional or bipolar transistor, as explained in 
Part 3, uses a current on its base terminal to control a 
flow of current between emitter and collectoi, and is 
characterised by an intrinsically low value of input 
impedance. With the field effect or unipolar transistor 
(f.e.t.), on the other hand, a voltage on the gate terminal 
controls a flow of current between source and drain, and 
input impedance is very high. 

The three basic circuit configurations of an f.e.t., 
common source, common drain, and common gate, 
behave in much the same way as common emitter, 
common collector, and common base bipolar circuits 
respectively. Like a pnp bipolar transistor, a p-channel 
f.e.t. has a negative supply voltage on its drain, and the 
^-channel f.e.t. is orientated as an npn device. There 
are two types of f.e.t. construction: junction and 
insulated gate. 

A figure for the d.c. gain of an f.e.t. is obtained from 
the ratio of a small change of drain current to a small 
change of gate voltage, called mutual conductance or 
transconductance (gm), and is expressed either as 
mA/V or /rniho, where 1,000 jimho = ImA/V. A 
typical g m for a junction f.e.t. is 4mA/V or 4,000 
//mho. 

Junction f.e.t. 

Looking at the diagram of an ^-channel junction 
f.e.t. in Fig. 7.4, a bar of «-type silicon is provided with 
source and drain connections at each end, termed 
"ohmic"* because the connections do not involve pn 
junctions and the bar behaves as a plain resistance. 
Two p-type silicon gate regions are formed on opposite 
sides of the bar to create a channel through which 
electrons moving from source to drain must pass. The 
gates make two pn junctions with the bar, having 
associated depletion regions as explained in Part 2. 

If a voltage is applied between gates and source, to 
reverse bias the pn gate junctions, the depletion regions 
—shown dotted in Fig 7.4 — will extend towards each 
other, making the channel narrower, and tending to 
"pinch off" a flow of electrons from source to drain. 
Gate input impedance is high because only a minute 
leakage current can pass through the depletion regions 
as long as the gate junctions remain in the reverse 
biased condition. It follows that external input biasing 
of a junction f.e.t. should be such that the gate is always 
maintained at a lower potential than the source, to 
preserve the depletion regions. 

The two separate gate regions of the junction device 
are usually joined together internally, but some f.e.t. s 
have independent gate connections to allow two input 
signals to be mixed together to yield a combined output ; 
see dual gate f.e.t. circuit symbol, Fig. 7.4. 

Insulated gate f.e.t. 

The insulated gate field effect transistor or i.g.f.e.t. 
(also called metal oxide silicon or m.o.s. f.e.t.) has a 
gate electrode which is completely insulated from 
source and drain by a layer of metal oxide, irrespective 
of input voltage polarity. There is also an extra 
terminal labelled "substrate" which can either be 
joined externally to the source, or may be used as an 
independent bias or input terminal. The gain of an 



798 



Practical Electronics October 1970 




*!!!•""!"" tm Cm I ■ Mil L/ U.vJ. I ("!"!""! 



CIRCUIT SYMBOLS 
«-, I0RAIN 



LOAD RESISTOa 

AAA 




:::| Fig. 7.4, N-channel junction field effect transistor 
III; and circuit symbols 



»; I.WXT. CIRCUIT 

SYMBOLS 



:::: gate 




DRAIN 



SUBSTRATE 



LOAD RESISTOR 



P-CHANNEL 
— | INDUCED BY 
SOURCE WHIAGEQNGATE 

P-CHAHNEt 




■ P'llll 

■ *■■ 
■HI 

■ ■•« 



Fig, 7,5a. Enhancement mode P-channe! i.g.f.e.t. 

LOAD REStSTOfl 

A/V . 

DRAIN | 
DEPLETION 
LAYER INDUCED 
BY VOLTAGE 
ON GATE V 





■■■■ 
■■■■ 



: Fig. 7.5b. Depletion mode P -channel i.g.f.e.t. 




::;: unijunction 
:::: circuit symbol 



■ ■■■ 

■ ■■■ 
*■■■ 

■ ■■» 
*■'■■ 

■ ■■■ 

■ ■■■ 

■ ■■■ 




«■■ m 

■ ■■■ 

■ ■■» 

■ ■■» 



■ ■■■ 

■ ■.■ 

■ ■■. 



■■■a 



::" Fjg. 7.6, Unijunction transistor 



i.g.f.e.t. usually lies somewhere between 0-5-2mA/V, 
slightly lower than for a junction f.e.t. 

There are two distinct kinds of i.g.f.e.t. In the 
enhancement mode there is no flow of current between 
source and drain when the gate is at source potential, 
A depletion mode device, on the other hand, has mean 
conductivity between source and drain when the gate is 
at source potential. 

Enhancement mode 

An enhancement mode p-channel i.g.f.e.t. is shown in 
Fig. 7.5a. Source and drain are formed by two p-type 
regions which are separated physically and electrically 
by an n-type substrate. For a current to flow between 
source and drain, the intervening substrate must be 
given ;?-type properties. How then is this achieved? 

Consider the gate electrode and substrate as the 
plates of a capacitor, separated by the oxide insulator. 
A negative charge on the gate electrode will induce a 
positive charge in the substrate by normal capacitor 
action, in effect replacing the w-type surplus of electrons 
with a /j-type surplus of holes directly under the oxide 
layer, and this forms a narrow channel linking source 
and drain. 

Because the enhancement mode device can only 
conduct as a result of a voltage on its gate, it is normally 
biased so that the gate is at about 0-5 K<w, or alternatively 
with the gate directly coupled to the drain of a previous, 
similar stage. 

Depletion mode 

The depletion mode /i-channel i.g.f.e.t. shown in 
Fig. 7.5b operates in the following manner. With the 
gate at source potential, electrical charges naturally 
present in the oxide layer will induce a narrow rc-type 
channel in the p-type substrate, thus linking n-type 
source and drain regions and permitting a current to 
flow. If the gate is made negative with respect to 
source, a depletion region will be induced in the channel 
and source-drain current will be reduced. 

The interesting thing here is that a positive voltage 
applied to the gate merely increases the width of the 
existing n-channel and promotes a greater flow of 
current between source and drain, without lowering 
input impedance, as would be the case with a junction 
f.e.t. or thermionic triode. So, the depletion mode 
i.g.f.e.t. can operate satisfactorily with zero external 
bias on its gate. 

UNIJUNCTION TRANSISTOR 

A unijunction transistor is a three terminal device 
with ontpn junction, which acts as a voltage controlled 
switch by changing from a high to a low impedance 
state when an input voltage reaches a set value. 

It can be seen from Fig. 7.6 that the structure of a 
unijunction resembles a junction f.e.t. with a single gate, 
but the mode of operation is quite different. A bar of 
n-type silicon has ohmic connections at each end — 
termed base 1 and base 2 — with a pellet of p-type 
semiconductor fused into one side of the bar to form an 
emitter region. 

If a voltage Vbc is applied to base ] and base 2, the 
bar will behave like a plain resistance, with a voltage 
gradient distributed along its length. Assume that the 
potential midway along the bar, in the vicinity of the 
emitter pellet is 0-5 V^, and that the bar resistance is 
represented by two equal resistances Rbi and /?b 2 - As 
long as the emitter potential is less than 0-5 Kt, c , the pn 
junction will be reversed biased and non-conducting, 
with a high internal impedance. However, if the 



Practical Electronics October 1970 



799 



THYRISTOR 



CIRCUIT SYMBOL 



ANODE 



GATE J _ 

CATHODE 




CATHODE 



LOAD 
RESISTOR 




Fig. 7.7. The thyristor and an equivalent circuit 
showing the principle of operation 



potential of the emitter should exceed 0-5 Kb C , the pn 
junction will start to conduct with forward bias, and in 
this condition the resistance of Ru x is lowered by a 
mechanism of hole injection from the emitter region. 
As Rbi grows smaller so current flow and hole injection 
increase, creating an avalanche effect which rapidly 
lowers emitter impedance. To reset the unijunction 
to its former high impedance state, the emitter voltage 
must be brought down almost to the level of base 1 
potential. 

The unijunction is often employed as a capacitor 
discharger in timing circuits. 



■ ■■*■■■■ 



CIRCUIT SYMBOLS I! 







TUNNEL 
DIODE 




FOUR LAYER 
DIODE 



ANODE 
GATE 



CATHODE 
GATE 



SILICON CONTROLLED 
SWITCH 



o £L J E -jL 



TRIAC 



DIAC 



Fig. 7.8. Circuit symbols of various other devices 



THYRISTOR 

The thyristor, or silicon controlled rectifier (s.cr.) is a 
three terminal, four layer pnpn device which conducts 
in one direction only, like a diode, when triggered by an 
input current. Because the thyristor has four semi- 
conductor layers and three junctions, with built-in 
transistor action, its operation is best explained by 
using a simplified model or equivalent circuit where two 
complementary transistors TR1 and TR2 represent the 
thyristor, as in Fig. 7.7. 

In the absence of an input current on the gate terminal 
(base of TR2), both transistors are switched off and no 
current flows between anode and cathode terminals. 
It can be seen that TR1 and TR2 are connected so that a 
flow of collector current in one will cause a flow of base 
current in the other. 

If a small positive input current is applied to the gate 
terminal, it will tend to turn TR2 on, and TR2 collector 
current turns TR1 on. As TR1 goes on, its collector 
current reinforces the gate input current (positive 
feedback), and so the circuit rapidly reaches the con- 
dition where TR1 and TR2 are holding each other fully 
on, and remain so when the gate input current is 
removed. In other words, the thyristor has a self- 
latching action, and can only be reset by removal of the 
anode supply voltage. 

If the battery of Fig, 7.7. circuit is replaced by an ax. 
supply, the thyristor will behave like a half-wave 
rectifier when a continuous gate signal is present, 
conducting during alternate half-cycles via the load 
resistor. When the gate signal is removed, the device 
turns off as soon as the a.c. potential reaches zero 
during a cycle, and then remains off until another gate 
signal is applied. 

So, the mean current flowing via the load resistor can 
be controlled by timed gate pulses, and this is the 
principle of one type of electric motor speed controller. 
The outstanding advantage of thyristors is that they are 
capable of handling large output currents at high 
voltages with minimum heat dissipation, and are there- 
fore useful for controlling mains powered equipment. 

OTHER SEMICONDUCTOR DEVICES 

There are, in addition to those already covered in this 
series, a few devices which have been designed to 
exploit some special semiconductor property, or are 
derived from more common devices, see circuit symbols 
Fig. 7.8 and following list. 

Zener diode. Variant of the silicon diode used for 
voltage stabilisation or as a voltage reference. 
Tunnel diode. Specially doped diode which can be 
made to function as an amplifier, switch, or oscillator 
at high frequencies. 

Varactor diode. Behaves like a small variable capacitor 
when biased by a variable reverse voltage. 
Four layer diode. A small, two terminal version of 
the thyristor; switches on when the anode-cathode 
voltage reaches a set value. 

Silicon controlled switch. A four layer device akin to 
the thyristor which has each semiconductor layer made 
accessible. Used for switching applications. 
Triac. Bidirectional thyristor used for full-wave 
control of a.c. currents. 

Diac. Bidirectional version of a four layer diode. 
Normally employed with triac in control circuits. 

This series of articles has attempted to introduce the 
beginner to basic principles in electronic components 
and circuitry. A wealth of more detailed information 
appears in some of our other published articles and in 
books usually available in public libraries. *fc 



800 



Practical Electronics October 1970 



1 



nN 



Ml 

OSE STEREO AMPLII 



Designed to provide the high standard of per- 
formance expected from modern sound repro- 
ducing systems, this amplifier has, in addition, 
microphone mixing facilities which extend the 
general usefulness of the equipment in the 
area of home entertainment and also make it 
suitable for discotheque and p. a. applications 




• 30W outpu 
• 20 W into 1512 
Disc, tape, rad 
• Mic. can be mixed 
• Truly complementary output 
• Full range filters and tone 
• Outputs open and short 
Low impedance stabil 
Two units in matchi 







e* C Vi^VI'd aV . f» At 



rt \\^ ef ' wo** 

<&}" c0 oV° to e 

\eC v ° %e ^ \,at»° . 



ALSO 
THIS ISSU 

SPECIAL SUPPLEMENT 
ON AUDIO EQUIPMENT 




A guide to hi-fi system planning. 
Deals with practical matters such 
as matching and connecting up 
the various items, from pick- 
to loudspeakers, and thi 




ELECTRONICS 



NOVEMBER ISSUE 
ON SALE 
OCTOBER 15 




G.C.T.V. Camera 



One of the latest constructional projects to be produced 
for schools and other teaching establishments by the 
Mullard Educational Service is a closed-circuit television 
camera. It can be built for as little as £45— claimed to be 
two or three times less than the cost of the cheapest 
professional camera. 

The camera uses a I inch vidicon tube which, together 
with the lens system, accounts for approximately 75 per 
cent of the total cost. 

It employs extremely simple basic circuitry, easy for the 
student to construct. No extravagant claims are made for 
the camera's performance, but given reasonable lighting 
conditions it will provide an output signal of 1 OV p-p 



Mini Computers Through Dealers 

Plans for the setting up of appointed dealers 
to market their low cost System 21 display 
terminals and computers was outlined at the 
official opening (July 29) of Viatron Computer 
Systems (U.K.) Ltd., at Finchley. 

Marketing will be handled through dealers who 
can provide supporting software systems and 
management consultancy associated with data 
processing. 

The basic System 21 terminal configuration 
includes a micro-processor with two Viatape 
recorders, which accept it ape cassette cartridges 
similar to those used ?on the entertainment 
market; keyboard; two? data channels and a 
video display. 

The 2111 Microprocessor has a main memory 
capacity of 400 characters. This 400-character 
memory is divided into five separate 80-character 
storage areas, designated as the READ record, 
WRITE record, MASTER record, CONTROL 
I record, and CONTROL 2 record. 

Integral to the microprocessor are four input/ 
output channels. Two of these internal data 
channels are devoted solely to reading and/or 
writing from one or two Viatape recorders. 



into 75 ft; capable of producing an acceptable picture on 
a TV monitor. The low impedance signal output further 
allows the distribution of the TV signal to other monitors 
at remote positions. At a recent press reception the 
camera was demonstrated and proved to give an excellent 
picture for its price and simplicity. 

A block schematic of the camera and preliminary 
information about the circuit are available now, A more 
forma! publication will be issued later in the year. Lin- 
stead Electronics will be marketing a kit for the camera as 
well as complete units. It is hoped that a modulator will 
later be added to the circuitry. 



The complete prototype Mullard camera made from readily available components for about £45 






Automatic Control 



The Norwegian fisheries research vessel "G.O. Sars", designed to 
meet future demands in fisheries investigation for the next decades, 
carries a computer data logging system, acoustical instrumentation 
and a complete machinery remote control console. All monitoring 
and bridge remote control equipment was supplied by Amund Clausen 
A/S. 

The remote control console is shown below; this console is linked to 
a slave console on the bridge and comprises control instruments, 
pressure and temperature measuring devices for all essential engine 
functions, engine speed, propeller speed and pitch monitoring and 
control for all four main engines. The engines are automatically speed 
synchronised before they are coupled to the reduction gear, load 
distribution and propeller pitch regulation to protect the engines are 
also automatic. 



Speed Radar 






Marconi Marine's new SAMI doppler 
Speed of Approach Measurement Indi- 
cator shown on the left in use on an oil jetty 
on the River Thames as a 100,000 ton tanker 
comes in to berth. Speed of approach is 
measured on the large meter in the upper 
cabinet and also on that in the lower cabinet, 
while a permanent record is simultaneously 
made showing direction of movement, as 
well as speed, on the graph recorder in the 
upper cabinet. The upper cabinet which 
contains all the signal processing circuitry is 
detachable and may be sited separately in a 
pressure proof hut. Information regarding 
the speed and movement of the vessel is 
passed to the pilot by v.h.f. radiotelephone. 

Now a very necessary equipment — with the 
size of ships increasing it is more difficult for 
the pilot to judge the speed of approach — the 
speed indicator can assist in the docking of 
all vessels in any weather conditions. 



Monitoring System 



An alarm, scanning and monitoring system, 
manufactured by Decca and called ISIS 
300, provides a standard range of instrumen- 
tation from which individual configurations 
may be selected for vessels ranging from 
yachts to supertankers. 

The photograph below shows an installa- 
tion in the 250,000 ton Esso Northumbrian 
the largest vessel built in Britain. The sys- 
tem's local scanning facility covers 120 points 
on the main machinery, cargo pumps and 
electrical generating equipment. 







ffl 




1 

1 


f > 

1 
1 

- v. J 



EGO™ 



Mu 



an 



ASSESSMENT OF HEARING IMPAIRMENTS By S. A. HARDY 



Electronics plays a very large part in providing 
diagnostic and remedial equipment for the hard of 
hearing. The hearing aid is widely publicised and 
advertisements for these devices appear regularly in the 
daily press. However, little mention is made of the 
diagnostic facilities available, for example, local 
medical centres and education authorities. Also it is 
seldom pointed out that a hearing aid should only be 
used if prescribed by an otologist (ear specialist) as in 
some cases a hearing aid would serve no useful purpose, 
or may be a source of great discomfort to the user even 
to the point of accelerating the degeneration of a 
hearing impairment. 

AUDIOMETER 

The measurement of the sensitivity of a patient's 
hearing under set conditions is of prime importance to 
the otologist who is making a diagnosis of a hearing 
impairment. 

A simplified block diagram of an audiometer is 
shown in Fig. 1. The audio sine wave generator may 
be of the continuously variable tuning type, or it may 
have preselected fixed frequencies which are based on 
the physical scale of C = 256Hz and not the British 
standard concert pitch based on A - 440Hz — where C 
would be 261-6Hz. The output from the oscillator is 
fed into an attenuator which is calibrated in decibels 
against laboratory standards. All extraneous equip- 
ment, such as the headset and bone conduction trans- 
ducer, are included in the calibration process. 

Signals are passed from the attenuator into a linear 
frequency response amplifier which drives either the 
headset or a bone conduction transducer, probably of 
the type shown in Fig. 2. The headsets used are of the 
type which exclude external noise, also the earpieces 
may be independently selected so that whilst one ear is 



being tested the other can be fed from a masking 
(white) noise generator at a preset level. This avoids 
the possibility of erroneous results due to the tone being 
fed to the ear under investigation being heard by the 
other through bone conduction. 

The basis of the audiometric tests is to select at 
random certain frequencies and moving the attenuator 
from maximum attenuation to minimum. The patient 
presses a switch, illuminating a lamp on the audiometer, 
as soon as the sound becomes audible. The audio- 
metrician, not necessarily an otologist, then prepares a 
graph called an audiogram which in this particular case 
would show the patient's threshold to hearing. 

AUDIOMETRIC TESTS 

A few audiometric tests used in determination of 
hearing malfunctions, other than the threshold test 
mentioned in the previous paragraph, are outlined 
below to demonstrate the usage of the different 
transducers: 

(a) The Rinne test is conducted by placing a bone 
conduction transducer on the mastoid bone 
just behind the ear under test — the patient then 
indicates when a tone is no longer audible at a 
particular level. The tone is then fed directly 
to the ear at the same level and should be perfectly 
audible in the case of the healthy ear. The use 
of masking noise for the ear not under investiga- 
tion is necessary to avoid ambiguous results. 

(b) The Weber test is conducted with both of the 
patient's ears occluded to external noise and 
tones are fed to a bone conduction transducer 
placed on the centre line of the forehead. The 
patient then indicates the ear in which the tones 
appear. This test is used to prove the binaural 
function of the ears. 





128 256 512 1024 2048 2896 4096 5792 8192 1158' 
FREQUENCY IN Hi 



Fig. 3. Audiogram showing the critical area of 
hearing impairment 



A range of early horn hearing aids 



(c) The Gelle test is carried out by slightly increasing 
the air pressure in the external auditory meatus 
and simultaneously introducing a tone via an 
earpiece. In a normal ear the threshold of 
hearing slightly increases at frequencies below 
Ik Hz as the pressure is increased. This test is 
used to show seizure of the stapes. 

(d) The Bing test is used to demonstrate malfunctions 
of the middle ear mechanism. This test is 
carried out by placing a bone conduction 
transducer against the mastoid bone adjacent to 
the ear under investigation and the tone level is 
then turned down until inaudible, then the ear 
canal is closed off. The tone then becomes 
audible again in the case of normal ear. 

(The titles for the above list are of American 
origin.) 

HEARING AID REQUIREMENTS 

Most of the consonants in human speech have fre- 
quency products which lie in the range of I kHz to 
4kHz and an impairment of hearing in this frequency 
range renders speech unintelligible, especially in the 
presence of background noises. The audiogram 
(Fig. 3) shows the critical area below which a hearing 
aid becomes a necessity. For instance case A would 
find a hearing aid a necessity, even though the low 



frequency response of the ear is satisfactory. Whereas 
case B could get by without an aid because the impair- 
ment is over the whole frequency spectrum, but there 
is an improvement over the critical area of the audio- 
gram. 

HEARING AIDS 

There are many types of hearing aid available from 
reputable manufacturers. However, the circuits given 
in Figs. 4 and 5 are Mullard experimental circuits and 
the design considerations discussed are the same for 
both aids. Both circuits have TR1 (input) and TR2 
(driver) collector currents of approximately 250 micro- 
amperes, this being the lowest practicable value 
consistent with low noise level without signal clipping. 
Transistor TR3 in both circuits are class A power 
amplifiers and have standing collector currents of 
roughly 2'5mA to give outputs of about 0-5mW, 

The circuit in Fig. 4, though having more com- 
ponents, is able to cope with large variations in ambient 
temperature and by siting the volume control between 
the input and driver stages contact noise generated by 
the microphone is reduced. If a mercury cell (such as 
the Mallory RM625) is used; the decoupling com- 
ponents R3 and C3 may be omitted and the cell life is 
about 100 hours. This circuit gives an output of 
0-4m W for 5 per cent total harmonic distortion with an 



SoHl 





Fig. 4, Hearing aid circuit by Mullard 



Fig. 5. Mullard hearing aid circuit using a d.c. 
amplifier 



Practical Electronics October 1970 



The Audiorama headrest type hearing aid 

electrical frequency response that is fiat to within 
0-25dB between 100Hz and 4kHz. 

The circuit of Fig. 5 is intended for use in spectacle 
frames, hence the requirement of the minimum 
number of components. However, the d.c. coupled 
amplifier of this type relies on the feedback loop to 
govern the d.c. stabilisation of the transistors and their 
temperature dependent characteristics. Thus the choice 
of Rl and d are critical, as Ri sets TR3 collector 
standing current and C( affects the working frequency 
range of the circuit, A loss of 6dB at 1kHz is con- 
sidered permissible and a time constant of one second 
(RI x Ct) is required. The predicted electrical fre- 
quency response of this circuit is within l-5dB of the 
response level at 1kHz over the range of 300Hz to 
5kHz, However, the battery drain is slightly higher 
and the circuit has an ambient temperature limitation 
of to 39 degrees C, the ideal working point being set at 
25 degrees C. 

Hearing aid of the type shown in Fig. 6 




Both circuits have an approximate acoustic gain of 
50dB allowing for an overall air to air loss in the 
microphone and earpiece of 35dB. 

TRANSDUCERS 

Both circuits (Figs. 4 and 5) use electromagnetic 
devices for the microphones and earpieces. Two 
advantages of the electromagnetic device are that it is 
not affected by high humidity levels and it is less 
sensitive to contact noise than the higher gain crystal 
counterpart. Most hearing aids are designed to drive 
electromagnetic earpieces or bone conduction trans- 
ducers which are sometimes used for certain types of 
deafness. 

Some aids, such as the spectacle frame or behind the 
ear device, have the transducer mounted in the body of 
the aid with a small bore (|in internal diameter) 
flexible polythene acoustic coupling tube which 
terminates in a special acrylic perspex ear insert as 
shown in Fig. 6. Also the type of transducer that is 
fitted directly into the outer ear canal, though similar 
to the earpiece supplied with some transistor radios, has 
the ear insert moulded to fit the individual's ear for 
maximum efficiency and comfort. 

When a hearing aid is prescribed utilising either of the 
above inserts, casts are made by the consultant from 
which the insert is manufactured. This is done by 
filling the contours of the part of the ear where the 
insert is to be situated with a special compound. The 
compound consists of two chemical components which, 







ACOUSTIC COUPLING 
S TUBE 






PLASTIC INSERT 
— ** IN CONCHA 








HEARING AKT 


Xmm# 


^ACOUSTIC EXIT AT 
OPEHIHS OF EXTERNAL 
AUDITORY MEATUS 



Fig. 6. A hearing aid using an acoustic coupling 
from the transducer in the aid to the outer ear canal 

on mixing, are semi fluid but rapidly harden after a short 
period of time though retaining a certain amount of 
flexibility. This impression is then used to form the 
casting mould for the plastic insert. The process is 
much the same for the manufacture of dentures. 

It is not usually convenient to use a hearing aid all the 
time and some people do have hearing impairments that 
do not require the use of an aid. For this reason 
Audiorama (a member of the Plessey group of com- 
panies) manufacture a headrest for domestic usage in 
conjunction with television, radio, tape and disc replay 
equipment. The headrest (Fig. 7) also provides 
protection from the hazard of equipment using the live 
chassis a.c./d.c. technique. 

Future trends with the advent of integrated circuits 
should result in even smaller hearing aids with much 
improved frequency responses and power gains allowing 
for the limitations of acoustic feedback. ^ 

Practical Electronics October 1970 



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BPYIO 

BR.Y39 

BSX19 

BSX20 

BSX2I 

S5X26 

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BSX60 

8SX6I 

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BSY5I 

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BSY79 

BSY82 

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BSY95A 

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BSW70 

DI6PI 

DI6P2 

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GETI02 

GETII3 

GETM4 

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GETII9 

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GET887 

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GET890 

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GET897 

GET89B 

MAT 1 00 

MATIOI 

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MATI2I 

MCI40 

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MJ42I 

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MJ4BI 

MJ490 

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MJE340 

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MPS3638 6/6 

NKT0OI3 7/ 

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NKTI25 

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NKT135 

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11/6 
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17/6 
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OC20 

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OC35 

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OC4I 

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OC46 

OC70 

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OCI39 

OC 1 40 

OCI70 

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OC202 12/6 

OC203 8/6 

OC204 

OC20S 

OC207 

OCP7I 

ORPI2 

ORP60 

ORP61 

P346A 

T1P3IA 16/6 

TIP32A 19/6 

TIS34 



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I 1,6 
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T1S45 

TI546 

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TI553 

TI560 

TIS6I 

ZTXI07 3/6 

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ZTX302 4/6 

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ZTX500 4/6 

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ZTX504 12/6 



Pott & Packing l/6d p«r order. Europe S/-, Commonwealth {Air) 13/- 
Send 6d. stamp for price list. 



PANEL METERS 

36 Series-^FACE SIZE 42 * 42mm. All prices Tor 1-9 pieces. 
50nA. 37/6; IOOijA, 15/-; 200^A. 32/6; SOOuA, 27/6; SO-O-SQ/iA, 
35/-; IOO-0-IOOj4A, 32/6; 500-0-500/iA. 25/-; IMA. 25/-; 5MA, 
25/-; 10MA, 25/-; 50MA. 25/-: 100MA, 25/-; 50OMA. 25/-; 
IA, 25(-: 5A.25/-; 10V, 25/-; 20V, 25/-; SOV, 25/-; 300V. 25/-; 
500V, 25/- 



SILICON RECTIFIERS 



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IA 
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OA70 


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MAINS TRANSFORMERS 

1 amp Charger. Sec. Q-3-5-9-I7V 

2 amp Charger. See. 0-3 -5-9- 17V 

1 amp (Douglas) MTI03 Sec. tappings from 6V to SOV 

2 amp [Douglas) MTI04 Sec. tappings from 6V to SOV 
Post and backing 4/6, 

5 amp (Douglas) MTI07 Sec. tappings from 6V to SOV 
Post and pocking 7/6. 
Various other Douglas Transformers ranging from iA to 5A in 
stock (details in catalogue). 



19/6 
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42/6 

110/- 



TRIACS 

5C4IA6amp IO0V 
SC4 1 B 6 amp 200V 
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40512 (RCA) TO-5 mod. 6 amp 400V 
40430 (RCAJ TO-66 6 amp 400V 
40466 (RCA) TO-5 mod. 6 amp 4O0V 
Economy Range Tria.cs 
TC4/I0 (Pressfit) 4 amp 100 PIV 
TC4/20 (Pressfit) 4 amp 200PIV .. 
TC4/40 (Pressfit) 4 amp 400 PIV 
TC3/40 (TO-5) 3 smp 400 PIV . . 
ST2 DIAC . . 



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SA — 11/- 13/- — 

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Also I2A. 100 PIV. '" 



400 
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VEROBOARDos 01 

Matrix Matrix 



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NORMAL PRICE 17/11. OUR PRICE 12/- 
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PLEASE NOTE. DUE TO BULK BUYING WE CAN NOW OFFER 
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INDUSTRIAL DISTRIBUTOR PRICES. NEW QUANTITY PRICE 
LIST NOW AVAILABLE FOR INDUSTRIAL USERS UPON 
REQUEST. ' 

"capacitors 

A large and comprehensive 
range available: Electrolytic, 
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styrene, Silver Mica, Tantalum, 
Trimmers, Tuners. 
Examples: 
2,0O0mF2SV, 8/6 
2,500m F 50V, 13/6 
3.000m F 25V, 10/6 
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WIRE-WOUND RESISTORS 

2 S watt 5% (up to 270 ohms 

only), 1/6 
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10 watt 5% (up to 25k [] only), 

2/6 

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Carbon: % 
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stock. Please enquire. 



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4/3 
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5- 



4/9 
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of 50) 
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HEAT SINKS 

4-8 v. 4 :•: I in Finned for Two 
TO-3 Trans., 9/6. 4-8 v. 2 x I in 
Finned, for One TO-3 Trans., 
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I/- Finned. For TO- 1 8, !/- 
Finned, For TO- 1 8, I/- Finned. 

RESISTORS 

Carbon Film 

i watt 5%, 3d. 
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I watt 5%, 5d. 

1 watt 10%, 6d. 

2 watt 10%, 1/3 



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Telex 21492 



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Cata' 



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808 



Practical Electronics October 1 970 



THE SOLAR ECLIPSE OF 1970 

The eclipse of the sun on March 7 
this year was perhaps the most 
important in the history of 
astronomy. The extensive tech- 
niques of all the disciplines associated 
with astronomy and space environ- 
ment has brought a wealth of data 
for analysis. Though much of this 
data will take some time to evaluate, 
a good deal of preliminary infor- 
mation has been given out from 
various sources. This information 
is mainly concerned with the corona 
and the effects observed in the 
ionosphere. 

Before the advent of the Lyot type 
of coronagraph, astronomers had to 
rely on the eclipses for observation 
of the corona. It is still -true that 
only at the time of the eclipse can 
the best observations of the visual 
corona be made. To this is 
added the techniques of radio astro- 
nomy, rocketry and other space 
research methods. The eclipse this 
year was therefore a considerable 
adventure with the very impprtant 
advantage of cross correlation of 
data. 

There was an important prediction 
of the shape of the corona as it 
would be at the time of the eclipse 
by K. H. Schatten. This prediction 
was based on the measurements of 
the photospheric magnetic field in 
the weeks that immediately preceded 
the eclipse. A number of the 
predictions were fulfilled particularly 
the presence of large helmet type 
streamers. 



SPACECRAFT EXPERIMENTS 

However, in other respects there 
were a number of predictions not 
observed and it would seem that the 
deductions based on spacecraft ob- 
servations need modification in the 
light of this eclipse. Rocket obser- 
vations had been made on a number 
of occasions before the eclipse using 
a coronagraph. Special experiments 
carried out by the Naval Research 
Laboratory of Washington made use 
of an Aerobee rocket launched from 
New Mexico two hours after the 
eclipse. 

One important observation was 
directed to the examination of white 
light corona at 3 solar radii. 
Normally when using earth based 
telescopes this area of the corona is 
difficult to observe. 

The Los Alamos Scientific Labora- 
tory made airborne observations of 
the corona, the chromosphere and 
geophysical observations of the en- 
vironment during the eclipse. The 
aircraft fiew at a speed of 508 knots 
at a height of just over 36,000 feet. 
The observations were thus enabled 
to be carried out for a period of 5 
minutes 30 seconds which was two 
minutes more than for earth based 
instruments. 

A very comprehensive experiment 
using five spectroheliographs were 




flown on an Aerobee Rocket from 
Wallops Island. This was fired into 
the eclipse path to photograph and 
scan the ultraviolet and the XUV 
flash spectrum electronically. 

Unfortunately, only part of the 
data was found usable in the form of 
a film in a cassette. The whole pay- 
load sank into the Atlantic because 
of the malfunction of the recovery 
system. The payload was recovered 
by the Naval Research and Develop- 
ment Salvage unit. 

The recovery was on March 22 and 
it is thought that the cassette which 
was coated in Teflon owes its survival 
to the slowing down of electrolysis 
by the presence of the Teflon. 

ECLIPSE EFFECTS 

The effects in the ionosphere of 
the solar eclipse showed a reduction 
of the electron content of the "F" 
layer by as much as 30 per cent. 
There were a number of effects in 
the ionosphere on radio propagation 
over a very wide range of frequencies. 
Satellite transmissions have yielded a 
great deal of data so that it will be 
some time before the final conclusions 
can be drawn. 

Measurements were also made at 
very low frequencies in region of 10 
to 20kHz; three phase changes were 
noted. At even lower frequencies, 
1 to 10kHz, some extraordinary 
phenomena appeared. During and 
for about an hour after the eclipse, 
"risers" were noted at l-8kHz and 
2-4kHz. Risers are musical tones 
of rising frequency. 

A number of suggestions have been 
put forward as a tentative explanation, 
all of which involve the "D" layer 
which is also very much reduced in 
density during total eclipse. 

Certain travelling ionospheric dis- 
turbances that were observed may 
be caused by gravity waves. The 
timings of certain oscillations show a 
near agreement with the possible 
effects of the cool shadow of the 
moon moving at supersonic speed 
across the atmosphere and generating 
gravity waves as suggested by 
Chimonas and Hines. 

MARINER TO VENUS AND 
MERCURY 

The launch in 1974 of the Mariner 
with two objectives, Venus and 
Mercury, will carry seven experiments. 



These have been chosen from the 
40 or so suggestions that were put 
forward. The total . payload will 
be 1 13 pounds out of the total weight 
of the probe which is 900 pounds. 

The probe will swing by Venus in 
1974 at a distance of about 3,300 
miles and will then proceed toward 
Mercury under gravity alone to pass 
the planet at a distance of some 630 
miles a month later. 

With the completion of the other 
two large dishes at Madrid and 
Canberra, there will be continuous 
contact by television and telemetry 
direct to earth. This means no 
storage on tape and re-transmission. 
All events recorded will be in real 
time. Many more pictures will be 
transmitted and it is expected that 
some 5,700 frames will be transmitted 
of Venus and 2,700 of Mercury. 

It is hoped that the ultra violet 
"clouds" which circulate round Venus 
every five days will be observed. 
The infra red radiometer will look 
for "holes" in the Venusian cloud 
cover. The photographs of Mercury 
should reveal whether it has satellites 
and also whether there are any 
special features on the surface. 
There will also be an ultraviolet 
spectrometer which will determine by 
solar occultation whether Mercury 
has an atmosphere. 

The occultation of the two trans- 
mitters will provide data as to the 
mass and radius, and whether it has 
an atmosphere and an ionosphere. 

The magnetic fields near the planets 
and the particle densities will be 
measured by other experiments 
aboard the spacecraft. 

MOONQUAKES 

Every month, when the moon comes 
to its closest point to the earth, it 
suffers a slight quake. This occurs 
every 28-2 days and the seismometer 
set up by the Apollo 12 crew has 
been sending continuous signals 
since last November. It is from the 
strong and weak signals that this 
new state of the moon has been 
derived. Identical patterns appear 
at the time of the closest approach 
each month. 

It has, of course, been known for a 
long time that the moon bulges 
toward the earth about one metre at 
this time. These results also confirm 
that the moon has residual heat. 






Practical Electronics October 1970 



809 



By i. n. watt 




SUITABLE FOR PHOTOGRAPHIC COLOUR PROCESSING CONTROL 



Colour printing is becoming more and more 
popular with .amateur photographers. In this 
process it is vital that the enlarger lamp output remains 
constant despite mains voltage fluctuations, for not only 
will the density of prints be affected by any changes, 
but colour balance will be altered also. 

Since correct colour balance is probably the most 
difficult characteristic to achieve in printing, it is worth 
while to go to some trouble to eliminate as many 
variables as possible. A constant light output from 
the enlarger lamp will certainly go a long way towards 
achieving this. 

In black and white printing also, a stable light level 
will assist in producing consistent results. 

CONSTANT VOLTAGE 

Probably the best method of ensuring a constant 
level of illumination is to run the enlarger from a con- 
stant voltage transformer — indeed, this is done in 
commercial colour printing laboratories. However, 
the cost of such a transformer could approach that of 
the enlarger itself. 

The alternatives are either to work in the darkroom 
at times when mains voltage fluctuations are at a 
minimum, or use a resistive dropper in series with the 
enlarger lamp. 

The resistance of the dropper is adjusted to give a 
constant voltage across the lamp. Since this voltage 
can be no higher than the lowest mains voltage ex- 
perienced, a lamp of a lower rating is sometimes used, 
although as enlarger lamps are normally arranged to 
be overrun in any case, the light loss is often acceptable. 

The disadvantages of a system using such a resistor 
are fairly obvious. It is wasteful, since excess voltage is 
spent as heat, and a large unwieldy resistor is required 
to achieve this dissipation. 

SOLID STATE CONTROL 

The use of some kind of solid state semi conductor 
device seems to be called for, and it is actually quite 
easy to construct a lamp dimmer control using a 
thyristor and a bridge rectifier. This would remove 



the objections of large bulk and the need for the dis- 
sipation of heat. 

A further improvement is the use of a triac with a 
saving in components, for no bridge rectifier is then 
needed, to obtain full wave control. 

TRIAC 

Many readers are no doubt familiar with the opera- 
tion of the thyristor in control applications. The triac 
operates in principle like the thyristor. When triggered 
into the conducting state by a suitable gate signal it 
will remain so until the current through the device is 
reduced to less than the holding current. 

It is different however, in that it can conduct in 
either direction on application of a positive or negative 
gate signal. Having three electrodes and bilateral a.c. 
operation provides the derivative, triac, from rr/ode, 
a.c. 

In Fig. 1 is given the circuit of the controller. The 
symbol for the triac is that of two thyristors in inverse 
parallel. Because of its bi-directional properties MT1 
and MT2 are used in place of anode and cathode, MT 
being the bi-directional anode, or more commonly 
termed "main terminal". 

Integral to this particular device is a diac, or bi- 
directional trigger diode. The symbol for this logically 
enough is two diodes in inverse parallel. The input to 
the diac is the gate input which controls the triac in 
phase with the load current. 

TRIGGER INPUT 

The capacitor and resistor network preceding the 
triac gate make up a phase control circuit. By varying 
VRI the phase angle at which conduction begins may be 
varied. The n arrangement of C4, R6 and C5 in 
combination with VRI, forms a circuit with a double 
time constant which provides smooth control from low 
to full power. 

When the voltage on the gate capacitor exceeds the 
breakover voltage on the trigger diode this conducts 
and switches the triac on for periods in the positive and 
negative half cycles. The length of these periods is 



810 



Practical Electronics October 1970 






Many New Models ! 

in the FREE 

HEATHKIT 1971 Catalogue . . 





CONSUMER 



HI-FI & AUDIO 



Here's the bumper Heathkit catalogue for you. Read about the wonder 

and fascination of kit building ... see in full colour the world's best 

values in Hi-Fi Radio, and even model radio control. Get up to 

date with what's new in scientific instrumentation . . . instruments 

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every purpose, in every walk of life. A wealth of information 

is all yours for the price of a postage stamp, in the Free 

Heathkit Catalogue. 




MARINE 



it No previous knowledge of elec- 
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if The constructional manual 
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Many other models in wide range 



=** HEATH (Gloucester) LTD., GLOUCESTER GL2 GEE 



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25/10 



Post Code 



Practical ELlectionics October 1970 



811 



MONO TRANSISTOR AMPLIFIER 



HSL.700 




A really high 
fidelity mon- 
aural ampliflr E 
with perfor- 
mance charac- 
t eristics tn suit 
the roost dis- 
criminating lis- 
tener, if tran- 
sistor circuit 
with integrated 
preamp! liter 
assembled on 
•peci.il printed 
sub panel. 

AD1SI-AD1C2 operating ii 
symmetrica) complementary 
pair. Output transformer coupled to 3 ohm and 13 olnn 
speaker Buckets. Ntandard phono Input lockets. Full 
wave bridge rectiller power supply for a.e. mains 200- 
240v. Controls: bass, treble, voiu roe/on /off. Function 
■elector for FU1, PCS, tape, radio. The Hs-iL.700 is 
utrongly eiiiifclructed mi rigid stcr! chan™ bronze hammer 
enamel finish, size Pj 5 41 in. hiKh. 
Sennit hit v — FF1— 50m,v, 5iSK input iiii|iw Inner. 
PC2- lllliii . v, I iin'P input Impedance. 
Tape- llOm/v, 1 meg input impedance. 
Rail in — llum/v , 1 i neg input Impedance. 
Output pmver measured at lite— 0-2 watte RMS into 
a ohms, OS watts KMS Info 13 ohm. Overall frequency 
response ;i0e/s-18Kc.fs: Continuously variable lone 
controls: Bass. +8db to — 12db at 100c/«. Treble, 
+ 10db to — lOdb at lOEc/s. 

The HSili.700 has been designed for true hitch fidelity 
reproduction from radio tuner, gramophone deck and tape 
recorder preamp. Supplied ready built and tested, com- 
plete with knobs, attractive anodised aluminium front 
escutcheon panel, lone spindles (can be cut to suit your 
housing requirements) full circuit diagram and operating 
Instructions. >«y i* / 

DDK SPECIAL PRICE £ I . I T.O. *• * '' "'«■ 

LOUDSPEAKER BARGAINS 
3in 4 uhm 10i-, P. i P. 1/8. SB 3 ohm 16/-, 1'. * *'• $>■ ■ 
7 ;•: 41n 3 ohm 81/-, F ft P, 4/ .IP tiin 3 or 15 ohm 85j'-, 
F. & P. 6/-. E.M.I. 8 I Bin a ohm with high flux magnet I 
tf/-, P. * P. 4/-. E.M.I. 13J 81n 3 ohm with high 
flux ceramic magnet 48/-, (15 ohm 4S/-), P. & P. 6/-. 
B.M.I. 13:; Bin, 3 or 15 ohm with two inbuilt tweeters 
and crossover network 4 gai, P. * P. 6;'-. 
BRAND MEW. 12ln low H/D Speakers. It or 15 ohm. 
Current production bv well-known British maker. Jow 
with Hiflui ceramic fcrrobar maenet assembly £8.10.0. 
Mf. 7/6 . Guitar models: 25 w 16,10.6. 35w £6.16.6. 
E.H.I. 3 1 in HEAVY DOTY TWEETERS. Powerful 
ceramic magnet. Available in a, 8 or 15 ohm 18,'fl each, 

v. & f, a/6. 

liin ■RA" TWIN CONE LOUDSPEAKER 
10 watts peak handling. 3 or 15 ohm, 87/6, P. & F. t) ■ 
86 OHM SPEAKERS. 3jin 14J-. P. A F. ";<i. 

VYNAIR AMD REXINE SPEAKERS AND CABINET 

FABRICS app. 34in. wide. tsuatly 35/- yd., our price 16, - 
yd . length. T. & P. 3;Q <mln. 1 yd.). S.A.E. for eampiee. 

KASHA VOX DESK TYPE MOVING COH, MICROPHONE. 

Medium impedance. Brand New -Special Price 48/-. 
P. & T. 2 ■'-. 

BALANCED ARMATURE EARPHONE 
Appro*. "0 ohm impedance. Can be used as ultra BUMtliva 
mike or speaker, ONLY 3,6. F. •£ P- 1/6 
CRYSTAL HIKES. High in™, for desk or hand use. 
High sennit ivity, 18,6. P. * F, 1/6. 
HIGH IMPEDANCE CRYSTAL STICK HIKES, or It 
PRICE 81-. P. A P. 1,6. 

HIGH IMPEDANCE DYNAMIC STICK MISES. High 
senaitivitv. 89/6. P. ft P. 2/0. 



STOCKISTS OF SINCLAIR EQUIPMENT 
Z.3U Amplifier 89/6. P. & P. 2/fi. Stereo 00 Prc-,Amplltier 
89.19 8. F. & P. 5,'-. PZ5 Power Kupplv £4.19.6. V. * P. 
3/6. P2<3 Power Supply £7.18.6. P. * P. 3'6. IC.10 
Integrated Circuit 59/6. P. &. P- 2 -. 



SPECIAL OFFER! PLESSEY TXPE 88 TWIN TORINO 
GANG. 400pF -: I4CpF. Fitted with trimmers and 
5;1 integral slow motion. Suitable for nominal 470 kc/s 
l.F. Size appro*. 2 1' liin. Only. 8/6. !'■ .V P. 2,'o . 

HONEYWELL HICROSWITCHES 8/P. C/O, Push-button 
action. Rating 2S0v. AC at 15 amps, biz* appro*. 
11": }~ J-. 5/- each . T. t P. ],'• ('lor more post free) . 

TELESCOPIC AERIALS WITH SWIVEL JOINT, Can be 
angled anil rotated in any direction. 18 section Heavy 
Chrome. Ks tends front 7' to appro*. -X". Maximum 
diameter (". 10/- each, P. & P. 1/(1. U section Lacquered 
Brass. Extends from 6* to approi. 391". M.-nimum 
diameter j*. 5/- each. F. & P. 1,'-- 



BRAND NEW MULTI-RATIO HAIRS TRANSFORMER S. 
Giving 13 alternatives. Primarv: O-210-24flV r . Secon- 
dary combinations: 0-5- 10-1 5- 2U -25-30-35- 40-«0V half 
wave at 1 amp or 10-0-10, 20-0-20, 30-0-30V. at 2 amps 
ful! wave. Si2e 31nL 3!inW 3inH. Price 34-. 
P. 4 F. 0/-. 

HAIRS TRANSFORMER. For trmalstot power supplies. 
Pri. SO0/24OV. Sue. !<-ri-!l at iOUinA. 14'-. I'. A P. 2/ii. 
Pri. 2OO/240^". Sec. 12-0-12 at 1 amp. 17/6. P. & P. 2/G. 
Prl. 2O0/240V. Sec. 10-0-10 at 2 amp. 27/6. 1*. A- P. 3/«. 
Tapped Primary 200 ■• 220-240 V. Sec. SI 4? at 500mA. 
18/6. P. 8 P. 2/G, 

BATTERY CKAROER TRANSFORMERS. 200/240V. 
input. Nominal output for 6 or 12V. batteries :l amps. 
Size approx. 3 _ : 2 1 y 2|in. Brand Xew. Price 81/-. 
P. & F. BJ-. 

HIOH OSADE COPPER LAMDf ATE BOARDS 
8 . . x A In- FIVE for 16/-. P. 4 P. 2/-. 



SPECIAL OFFER ! ! 

HI-FI LOUDSPEAKER SYSTEM. BeiuliluUy made 
teak flnuh enclosure with molt attractive Tygan Iront. 
Siie 16" hieh l 10" wide 6" deep. Pit^d with 
E.H.I. Ceramic M*snet IS* 8' ban unit, two H.P. 
tweeter units and croieotrer. 

Power handlim- 10 watti. R Gnc L '' lrli ^« 

Aviiltble 3 or 15 ohm impedance. w **•■»• 10/- 



TRANSISTOR STEREO 8 + 8 MK II 

Now uniii£ Silicon Transistors In first five stages on each 
channel resulting in even lower noise lew] with improved 
sensitlvitv. A reallv first-class Hi-Fi Stereo Amplifier Kit. 
Uses 14 fraosislorlt giving 8 waits push pul! output per 
chniinri tlflW mono). Integrated prc-nmp. with Basa, 
Treble mid Volume controls, Suitable for use with 
Ceramic or Crystal caitridgm Output stage for any 
siieakers from 3 to 13 ohms. Compact design, all parts 
supplied incluilliis drilled metal work, Cir-KR board, 
attract hv front panel, knobs, wire, solder, nuts, bolts- 
no extras to buy. Khiiple step by step instructions enable 
anv constructor to build an amplifier to lie proud of. 
Brief specification: l-'rcq. response —SdB. 28-20,0O0c/s. 
Bass lwwst approx. to +12dIS. Treble "cut appro*, to 
— Hi. II',. Negative feedback 18dB over main amp. 
Power leiioireioents 25V" at 0-0 amp. 
PRICES: AMPidl'lEK KIT £10.10.0; POWER PACK 
KIT £3.0.0; CABINET £3.0.0, All Post Free, 
tleo available STEREO 10 -I- 10. As above but 10 watts 
per channel. PRICES: AMPLIFIER KIT £18. POWER 
PACK KIT £3.10.0. 

Circuit diagram, construction details nod parts Hat ifnc 
with kit) 1/6. (S.A.C.;. 



GENERAL PURPOSE HIGH STABILITY TRAN- 
SISTOR PRE-AMPLIPrER, For F.V, Tape, Mike. 
Guitar, etc., and suitable for use with valve or 
transistor equipment. 9-18V. Battery or from H.T. 
line 200f300V, Fic(iuc]ic\' response 1jHk-25KH^. 
Gain 2GdB. Solid encapsulation size l}xl|X)te, 
Brand new — complete with instructions. Price 
17/6. T. A P. 2;0. 




SPECIAL PURCHASE! 

E.M.I. 4-SPEED PLAYER 
Heavy SJin. metal tuintnble. 
Low flutter performance 200/ 
250 V shaded motor t00 V" 
tap). Complete with latest 
type lightweight pick-up arm 
and mono cartridge with t/o 
stvlii for LP/73. ONLY 
6S/-. r. A P. 0/G. 



(JDALITY RECORD PLAYER AMPLIFIER MK II 

A top-quality record player amplifier employing heavy 
ilutv double wound mains transformer, ECC83, ELS4. 
EZ80 valves. Separate Bass, Treble and Volume controls. 
Complete with output transformer matched for 3 ohm 
speaker, Size Tin. w. :. 3d. : 6 h. Ready built and tested. 
PRICE 75/-. P. A P. t>/-. AL80 AVAILABLE mounted 
on board with output transformer and speoker ready to 
lit Into cabinet below. PRICE 87,6. P. * P. 7.0. 
DE LUXE QUALITY PORTABLE R P CABINET MK II 
Uncut motor board sue 14 i r. 12lu.,(!le,'ir,'iucc2iu.below 
51 in. al>ove, Will take above aoiolifier and any B..S.K. m 
CARltAUD changer or Single Player (except AT0O and 
SP25). Wze 18 -13:: Bin. PRICE 79/6. P. A P- U.'G. 

10/1* WATT HI-n 

AMPLIFIER KIT 
A stylishly finisbed 
monaural amplifier 
with an output of 
14 watts from 2 
ELS4s in push-pull. 
Super reproduction 
of both music aii'l 
speech, with negli- 
gible hum. Scpara'.f 
inputs for mike and 
gram allow- record* 
and announcements 
to follow each other. 
Eullv shrouded sectlno wound outpui. nansformir to 
match 3-IoH speaker ami 2 independent volume controls, 
and separate bass ami treble controls are provided K'viug 
sood lift and cut. Valve line-up 2 EL84s. ECC83, EPS U and 
EZ80 rectifier. Simple instniclion booklet 8/6 (Free with 
parts). All paiti loldiepiratelr. ONLY £7.18.6. P. ft P. 8/6. 
4-lso available ready built and tested eoioplete with std. 
i nput sockets, £8.18.6. P. A F. g/0. 

BRAND HEW TRARSHTOR BARGAINS. GET 13 

(Matched Pair) 15/-; V15,'10p, 10,'-; OC71 6/-: OC7b «/•; 

AF117 3/6; 2G330 (SPN) 8/-. B „ 

Set of Milliard It transistors OC44. 2 OC4o, AC12SP, 
matched pair AC128 2S/»: ORFI'J Cadmium Sulphide 
Cell 10. 6. All post free. 

VERY POWERFUL COMPACT MOTOR 
For 12v. ]>.C. operation. Off load consumption approx. 
100mA. Totallv enclosed. Quiet in operation with high 
starting torque. Overall size approx. 1J"L :: II" dia. 
Free shaft A" dla. :: J"L. Iileal for Model Mukers, etc, 
ONIiY 7/6 each P. A P. 1/-. 
3 or more poet free (A few (>v, versions also available). 




DE LUXE STEREO AMPLIFIER 

mains 
00-240 volU. 
Using heavy 
duty fully 
i s o 1 a t o d 
mains trans- 
former with 
full wave 
rectification 
giving adc- 
tiuate smoothing 
th negligible hum. 
Yaive line up:— 2:: 
ECLSfl Triode Pentodes. 
1 EZtSO as full wuvs rectifier. Two dual potentiometers 
arc provided tot baas ami treble control, giving bass and 
treble boost and cut. A Muni volume control Is used. 
Balance of the leit and right hand ehamie.'s can be 
adjusted by means of a separate "balance" control fitted 
at the rear of the chassis. Input sensitivity is approvj- 
mately 300m/v (or full peak output of 4 o atts per channel 
(8 watts mono), into 3 ohm aper.kurs. Full negative 
feedback in a carefully calculated circuit, allows high 
volume levels In be U6W1 with n-gHgible distortion. 
Supplied complete with Uuobs, chassis size llin. w 4in, s. 
Overall height Including \'alves Sin. Ready built and 
tested to a high stand aid. Price 88.18.6. P. ft P. */-. 




4-SPEED RECORD PLAYER BARGAINS 

Mains models. AH brand new in maker's packing. 
LATEST B S R. C108.A21 4-SPEED AUTOCHANGER. 
With latest mono compatible cartridge £8.16.6. Cut. ''> <•■ 
With stereo cartridge £7.18.6. Cnrr. 0/0. 
LATEST GARRARD MODELS. AH types available 1085. 
208S, SP25. 3000, AT80 etc. Send S.A.E. lor Latest Prices I 
PLINTH trims cut out for (;arrard Models 1025,2025, 
2000, 3000, 3JO0, etc. With rigid transparent plastic 
cover. Special assign enables aba re models to be used 
with cover in position. Also suitable for housing AT GO 
and SP23. OUR PRICK £6,15.0 complete. P. ft P. 8/6. 



LATEST ACQS GP81/1SC Mono CompatlMe Cartridge with 

t/o stylus for LP/EP/7R. Universal mounting bracket. 

30/-. " P. & P. 1 li. 

SONOTONE 9TAHC nmtMlMe Stereo Cartridge with 

diamond stylus 60/-. P. & P. 2;-. 

LATEST R0HETTE T.O Slereo Compatible Cartridge fur 

UlVLP,'St«M0/T8, 38/6. P. & T. 2'-- 

LATEST EOrTETTE T/O Mono Compatible Cartridge for 

EP/LP/78 mono or stereo records on mono equipment, 

30/-. P. ft P. 2/-. 




HIGH GAIN 4 TRANSISTOR 
PRINTED CIRCUIT 
AMPLIFIER KIT 

Peak out- 
put in excess 
of 11 watts. 
All stan- 
dard British 
components - 
Built on 

printed circuit panel sUc (I : 3iu. 
Generous size Ui'ivcr and Output Transformers, Output 
transformer tapped for Jt ohm and 10 ohm speakers. 
Transistors (G ET114 or S 1 Mullard AC 128D and matched 
pair of AC128 o/p). volt operation. Everything supplied, 
wire, Lattery clips, solder, ,-tc. ivc easy to 

follow instructions and circuit diagram S/6 (Free with 
Kit). All parts sold separately. SPECIAL PRICE_*8/6. 
P. ft P. 3;-. Also ready built and tested ,86/- 



ft P. 3/ 



3-VALVE AUDIO 
AMPLIFIER HA34 UK II 

Uesigned for Hi-Fi reproduc- 
tion of records, A.C. Mains 
operation. Ready built on 
plated haivy gauge metal 
riL.isiis, -iff. T.'.iilw. :■: 4in. (I.:-: 
4 Jin. h. Incorporates ECC83, 
EL84, EZ80 valves. Heavy 
duty, double wound mains 
transformer and output trans- 
former matched for 3 ohm 
speaker. Separate volume, control and now with improved 
wide range tone controls giving bass and treble lift and 
cut. Negative feedback line. Output 41 watts. Front 
panel can be detached and lends extended for remote 
mounting of controls. Complete with knobs, valves, etc., 
wired and tested for onlv £4.15.0, P. ft P. 0/-. 




HSL "FOUR" AMPLIFIER KIT. Similar In appearance to 
HA34 above but employs entirely different and advanced 
circuit"-. Complete set of parts, etc. 79/6. P. & P. 8H 



HARVERSON-S SUPER MONO AMPLIFIER 

A super quality gram amplifier using a double wound 
mains transformer, EZ80 rectifier and ECL82 triode 
pentode valve as audio amplifier and power output stage. 
Impedance 3 ohms. Output approx. 3-5 watts. Volume 
and tone controls. Chassis size only Tin. wide :: 31n. deep '■'. 
Gin. high overall, AC mains 200/240Y. Supplied abjolutcly 
Brand New completely wired and tested with valves and 
good quality output transformer. FEW ONLY. 
OUR ROCK BOTTOM EC/. P. & P. 

BARGAIN PRICE oa / «/- 



Open 9-5,30 Monday 

to Saturday 

Early closing Wed. 1 p.m. 

A feie minutes from 6'on/A IVimbUd&u 
Tube SfattM 



HARVERSON SURPLUS CO. LTD. 

I70 HIGH ST., MERT0N, LONDON, S.W.I 9 t.i.ii.mmo 

SEND STAMPED ADDRESSED ENVELOPE WITH ALL ENQUIRIES 



(Please write clearly) 

PLEASE NOTE : P. ft P. CHARGES 
QUOTED APPLY TO U.K. ONLY. 
P. & P. O R OVER SEAS ORDERS 
CHARGED EXTRA. 



812 



Practical Electronics October 1970 




CONTROL 



LI JmH S1 <? r ,„, <B5 

FULL ^>10kfl 




™. . TRIAC 1 
lOOkA 40432 



I 

^4 |C5 

0-1fiF O-ljiF 



MTZ 
HT1 



Fig. I. Complete circuit of the triac tamp controller with meter circuit and interference suppression 



governed by the setting of VRI , the cumulative effect of 
which is to permit the power to the load to be varied. 

Typical load voltage waveforms for early triggering 
in the cycle are given in Fig. 2, Here, the power 
available would be near maximum. 

INTERFERENCE SUPPRESSION 

Improvements in the manufacture of s.cr.'s and 
triacs has resulted in faster turn on times. In the case 
of the 40432 triac used, this time is about 2 to 3 micro- 
seconds. Pulses with such short rise times are a 
source of radio frequency interference and some form 
of suppression is necessary. 

In the circuit, LI and C3 prevent interference being 
fed back via the mains leads. Radiated interference is 
kept to a minimum by mounting the components in a 
metal box, then earthing this. 

In practical tests carried out with a transistor radio, 
interference was only apparent with the radio held about 
a foot away from the completed controller. 

The inductor LI is made up by pile winding about 
400 turns of 26 s.w.g. enamelled copper wire on a small 
Aladdin coil former complete with iron dust core. 

Since this coil appears in series with the load there 
is a power handling limit df 200 watts. 

VOLTAGE MONITORING 

In order to be of value in enlarger lamp controlling, 
an accurate means must be provided for measuring the 
voltage applied to the lamp. Unfortunately, an 
ordinary moving coil voltmeter is calibrated for r.m.s. 
sine wave voltages, which is not much use for measuring 
the distorted waveshapes as given in Fig. 2. 

A "true" r.m.s. voltmeter would indicate correctly 
since lamp light output is strictly dependent on applied 
r.m.s. voltage; but such r.m.s. meters are expensive 
and not easy to obtain. 

METER CIRCUIT 

The meter circuit, which is in parallel with the load 
terminals in Fig. 1, was developed to overcome this 
problem and found to be not only accurate in use but 



to have an advantage over r.m.s. meters for the range 
of voltage employed. 

The diode Dl permits only positive going half cycles 
to charge CI. 

Rl and R2 prevent the circuit from becoming a peak 
reading voltmeter and in combination with CI effect a 
compromise between peak and average voltages to 
indicate true r.m.s. lamp output over the range 190 to 
250 volts. 

Since only this limited range is required, advantage 
is taken of the technique of expanding the meter scale 
with the Zener diode D2. The capacitor C2 removes 
the 50Hz ripple and gives meter needle stability. 

As the object of the meter is to maintain a steady light 
output irrespective of mains fluctuation, calibration is 
unnecessary as the only requirement is an arbitrary 
constant meter setting. 

CONSTRUCTION 

All of the components of the controller fit inside a 
4^in by 3£in by 2^in die cast box. This provides at 
once, a robust housing as well as electrical screening. 
Reference to Fig. 3 gives the complete prototype wiring 




Practical Electronics October 1970 



813 




To load 



Fig. 3. Wiring of the controller in a diecast box. The 
tag strips are shown removed from their mountings to show 
the connections of the triac mounted on the heat sink (note 
the two leads which connect to tags) 



COMPONENTS . . 







Resistors 

Rl 33kQ IW 

R2 [OkQ IW 

R3 ISkQ 

R4 22 a 

R5 iOkCl 

R6 tOkH 

All ± 10% i watt carbon except Rl and R2 

Potentiometer 

VRI lOOkQ wirewound 

Capacitors 

CI 0-\(iF polyester 
C2 47 (if elect. 6V 
C3 OOlfiF polyester 
C4 O'ljiF polyester 
C5 0*l/xF polyester 

Triac 

Triac I 40432 (R.CA.) with heatsink 

(Electrovalue, 28 St. Jude's Road, 
Diodes Englefield Green. Egham, Surrey) 

Dt ISII3 
D2 ZFI6!6VZener 

Inductor 

LI 3mH (for details see text) 

Meter 

Ml 0-1 mA f.s.d. moving coil 

Switch 

SI Single pole changeover toggle switch 

Miscellaneous 

Die-cast box (Eddy stone) 4^ in x 3^ in x 1\ in 
Aladdin coil former 4mm with square base, dust 

iron core, 26 s.w.g. enamelled copper wire 
Tag strip 



LOAD 




CONTROL 



Fig. 4. The substitution of a double-pole change-over 
switch for SI enables a neon lamp to be used os a full 
power indicator. 



814 



Practical Electronics October 1970 



TRANSISTOR RADIOS 
TO BUILD YOURSELF 

Backed by after sales service 



HEW! roamer eight mk 1 

WITH VARIABLE TONE CONTROL 

7 Tunabk Wavebands: Medium Wave 1, Medium Wave 8. Long Wave, Bi.W.l, is.W.'J, H.W.3, 
mid Trawler Bawl, Built lit ferrite rod aerial lor Medium and Long Waves. 5 section ill'lu chrome 
plated telescopic aerial lor Short Waves can be angled and rotated lor maximum performance. 
Push-pull output lining *WMw type transistors. Socket (or car aerial. Tape record socket. 
Detect I v It y switch. Switched UHJIUIUU socket euiuplete with earpiece for private listening, ft tran- 
sistor* (dim 3 diodes. Famous make 7 41n Bpeaker. Air spaced gauged tuning condenser, Onfoff 
switch volume control. Wave chance aw itch and toning control. Attractive case hi rich chestnut 
shade with gold blocking. Hlie 9:7 4fn appro*. Easy to follow instructions and diagrams 
make the Roamer Eight it pleasure to build. r»rts price list anil may build plane S.'- (EREE 
with parts). 



Total building costs 



£6.1 9.6 



p. & p. 

7/» 



roamer seven 
mk IV 




7 FULLY TV SABLE IV AVE 

BAN* US— M.W.I, M.W.'J, L.W., 

H.W.I, 8.W.2, N.W.3 and Trawler 

Band, Extra Medium waveband 

provides easier tuning of Radio 

Luxembourg, etc. Built in ferrlte 

rod aerial for Medium and Long 

Waves. Retractable 4 section 241b 

carom e plated telescopic aerial for 

peak Short Wave listening. Socket 

for Car Aerial. Powerful push -pull output. 7 transistors 

and two diodes including Micro-Alloy H.F. Transistors. Famous, maki 

7 4lu P.M. speaker. Air spaced ganged tuning condenser. Volume ,'on 'off control. 

wave change switches and tuning control. Attractive esse with carrvlrtg handle. Size 

9 x 7 y 4in appro*. Easy to follow instructions and diagrams mske the Rnamer 7 a 

pleasure to build. Parts price list and easy build plans 3 - (FREE with parts}. 



Total building costs 

£5.19.6 



P. 4 P. 
7/6 



Personal Earpiece with switched locket 
for private listening, 5/ - extra, 



pocket five 



MEDIUM WAVE, LONG WAVE 
AND TRAWLER BAND 
PORTABLE 
WITH SPEAKER 

Attractive black and gold case, ftlze 0] ■ 1 1 
J 'In. Tunable over both Medium and Lung Waves 
with ex tended M.W. baud tor easier toning of 
Luxemtourg, etc. 7 stages— 5 transistors and S 
diodes, supersensitive ferrlte rod aerial, tine tone 
moving coil speaker. Easy build plans and parts 
price list 1/6 (FREE with parts). 




Total building costs 
P. & P. 
3 6 



44/6 



roamer six 

SIX WAVEBAND PORTABLE 
WITH 3in. SPEAKER 

Attractive case with gilt fittings. Size 7 J . S' 
ljin. Tunable ou Medium and Long Waves, two 
Short Waves, Trawler Band pins an extra M.W. band 
for easier tuning of Luxembourg, etc. Sensitive 
ferrlte roil aerial and telescopic aerial for Short 
Waves. 8 stages- 6 translators and - diodes in- 
cluding Micro- Alloy B.F. Transistors, etc. (Carrying Total building costs 




strap 15 extra). Easy build plans and parts price 
list 'I!~ (FREE with parts). f .Vote : WA«i prttcnl 
atvtki of 1/kic cattt are tzltauttetl a rterr rnis ilmitar 
la " JVitmeigM '* will be tuppiitd.) 



79/6 



P. 4VP. 

4/6 



* Callers side entrance Stylo Shoe Shop 

* Open 10-1, 2.30-4.30 Mon.-Fri. 9-12 Sat. 




MEW! 

transeight 

SIX WAVEBAND 
PORTABLE WITH 
3in. SPEAKER 

Attractive case in black with 

red grille and cream knobs ami 

dial with polished brass 

inserts. Size 1) :; fjj :; U|lii, 

approx. Tunable on Medium ami Lung 

Waves, 3 Short Waves and Trawler Band. 

Sensitive ferrite rod aerial for M.W. and L.W. Telescopic aerial fur Short Wave 

8 improved type transistors plus 3 diode*. Push-pull output. Battery eci'nomiscr 

switch for extended battery life. Ample power to drive n larger speaker. Parts 

price list and easy build plans 6 - (FREE with partsl. 

Total building costs 

%M f^al lH '■ * ' Earpiece with switched docket fur private 
O s«7 / W 5 6 listening fi/- extrtt. 



transona five 

MEDIUM WAVE, LONG WAVE 
AND TRAWLER BAND 
PORTABLE 
WITH SPEAKER 



Attractive case with red speaker grille. M be til 

4iin Hi". 7 stages- 5 transistors and -2 diodes, Total building costs 
ferrite rod aerial, tuning condenser, volume control , jm w^m I ^% o i a 

fine tone moving coil speaker. Easy buiid plana and MM M I BE r . * r 

parts price list l.'fl (FREE with partsl. ""sP I / ^gf 3/9 




RADIO EXCHANGE LTD 



61a, HIGH STREET, BEDFORD. Tel. 0234 52367 

I enclose £ please send items marked 

ROAMER EIGHT □ ROAMER SEVEN □ 
TRANSEIGHT □ POCKET FIVE Q 

TRANSONA FIVE □ ROAMER SIX Q 

Parts price list and plans for ' 

Name | 

Address 

PE22 

L I 






Practical Electronics October 1970 



815 



BSR 4-SPEED SUPERSLIM 
AUTO RECORD CHANGER 

Plays 12". 10" or 7" records 
Ante or Manual. A high 
I ai lit t unit backed by BSR 
reliability with IS months* 
joarantee. E lie 13| 
lliin. Above 
motor board 3 Jin, 
below 2fin. AC 200 Z50v 

Foil 

s:- 

Transcription 
Auto Changer. Calibrated Stylus Pressure. 
BSE Minichioger UA50 Stereo. Mono. 
Flays IB", 10" or 7" record*. 

Site IS - 8: in. AC E00 BSOv. Post 5/-, 



With STEREO MOHO XTAL 
BSR TJA70 Stereo; Mono 




£14 

£8 



SABRARD PLAYERS with So no lone 91 A Cartridge!. 
Stereo Diamond Mono Sapphire. SPSS Mlt II £15. 
ATM Hk II fl5. Model 30OO £13. Pott 5-. 
RECORD PLATER PORTABLE CABINET 7C;. 

Spice lor amplifier and autochanKer. Post 5.'-. I 

RCS DE-LUXE 3 WATT AMPLIFIER. Ready made tested, 
2-stage with triode pentode valve, 3 watti output. Tone and 
volume controls. Isolated maim transformer. Knobs, 
loudspeaker, valves ECL8B, EZ80. Response fA 

60-12,000 cps. Sens itivity 200m V, Foit 6. . 
RCS 2 WATT AMPLIFIER with loudspeaker and 
vllve UCL8B. Pott 5,'-. 



£3 



R.C.S. TEAKWOOD BASE Reidy cot out lor 77 ,'i 
mounting (state player make and model). * * / w 

R.C.B. PLASTIC COVERS FOR ABOVE BASE. 77 >A 

Durable tinted plastic, atiractjve appearance. * * .'" 



EMI PICK-UP ARM. Complete with mono cartridge 29/6. 
EMI JUNIOR 4 SPEED RECORD PLAYER. Mains £■} 
operated motor, turntable and pick up. Post 5: -, 

HI-FI PICK UP CARTRIDGES 
OP94 65-; OF93 45.-; GFfil 30-; GF67 19 6, ACOS 
L.P. only 10, 6. All standard fixing complete with stylos. 



CRYSTAL MIKE INSERTS 

It" dia. 8,8, ACQS IT dia. 12 6. BM3, 1' dia. 9 8 

PORTABLE A 

Portable mini p.a. system. 
Many uses — ideal lor 
Parties, or as a Baby 
Alarm, Intercom, Tele- 
phone or Record Player 
Amplifier, etc. Attractive 
re line covered cabinet, 
lire 12 y s :: tin., with 
powerful 7 - iin. speaker 
and font transistor one watt 
power amplifier. Uses ppb battery 
Brand new with lamous makers' guarantee 
Fort o 

YVEYRAD P50 — TRANSISTOR COILS 




RA2W Ferrite Aerial 

Ose, F501AC 

IT. F50 2CC 470 kc's . 

»rd I.F. PSOfSCC 

Pfil/1 or F51/2 

F61/3 

FerrlUHodS Jin. 4/ 



13/- I Spare Corea , fit', 

, .6/- Driver Trans. LFDT4 . . 10;- 

6,7 ! Printed Circuit, PCA1 . . 10.'- 
..917 I.B. Tuning OauK 10/8 

8/7 I Weyrad Booklet 8/- 



, 9/7 1 OPTl 
6 - iin. 5/' 



,11' 



VOLUME CONTROLS! !2.f* ^?** d s " 

Lou* spindles. Midget Size *«™ f £™ c ED 
S K. ohms to 2 Meg. LOG or I AEHAXIAL-AIR SPACED 
ILTf. L'S 3,'-, D.P. 5- 40 yd. 28-: 80 yd. 40/-. 
STEREO L'S 11/-, D.F. IS- , FRINGE LOW LOSS 7 
Edge 5K. S.P. Transistor, 5,'-. I Ideal 825 lines *< 



yd. 



WIRE-WOUND 3-WATT POTS. I WDIE- WOUND 3-WATT 

Small type with small knob, STANDARD SIZE POTS. 

Values 10 O to 30 K., C LONG SPINDLE O / 

J i~ I in (1MTWS InlMK ",i 



Carbon 80 K to 2 mec 



| 10 OHMS to 100 K. °r 



VEROBOARD 0-lfi MATRIX 
21 :• din. 3/8, 2) ■ 33 in. 3/3. 31 3jjn. 3 8. SJxSin, 5/2. 

EDGE CONNECTORS 16 way 5/-: 24 w ay 7/6. 

FINB 36 per packet 3,4. FACE CUTTERS 7/6, 
S.R.B.P. Board 015 MATRIX SSln, wide «d. per lin., 
Siin. wide 9d. per lin.; Bin, wide 1/- per lin. (up to 17ln.). 

I.R.B.F. nndrill cd Am. Bo ard 10 Bin. 3'- . 

BLANK ALUMINIUM CHASSIS. 18 a.w.g. Siin, sides, 
7 x 4in., 6/-; 11 ; 3in., 7/8; 11 : : "in. 9/6; IS k Bin., 10/8; 
IS x 14lu„ 15/-; B ■■< 7 X 2in„ 8/8; 14 xtt X 2in., 14/6. 
ALUMINIUM PANELS 18 a.w.g. 12 « 12in. 6/6; 14 v. Bin. 
6/6; 12 v Bin. 4.6; 10 "in. 3.6; 8 Bin. 2.6; 6 4in,, 1 6. 

Hinoh DIAMETER WAVE-CHANGE SWITCHES. 2 p. 2- 
way, or 2 p. 6-wny. or 3 p. 4-way 4,6 each. 1 p. IB-way, or 
4 p. 2-way, or 4 p. 3- wiy 4/6 each. 1 inch DIAMETER 
Wavechange "MAKITS" 1 p. 12-way, 2 p. 6-way, 3 p. 4- 
way, 4 p, 3-way, 8 p. 2-way. 1 water 12/-, 2 water 18;-. 3 
wafer 24/-, 4 waler 30/-, 5 wafer 36/-, 6 wafer 42/-. 
TOGGLE SWITCHES, sp.2/6; sp. dt. 3,6; dp, 3/8; dp, dt. 4/6 



ALL PURPOSE HEADPHONES 

H.R. HEADPHONES 2000 ohms Super Sensitive. . 36,,- 

LOW RESISTANCE HEADPHONES 3-5 ohms 39/6 

DE LUXE STEREO HEADPHONES 8 ohms 85/- 



• GENERAL PURPOSE TRANSISTOR j 

PRE AMPLIFIER BRITISH MADE J 

lor Mike, Tape, P.U.. Guitar, 
Battery 9-12v. or H.T. line 200-300v. D.C. Operation. Si 
1! 11" 1 . Response 25 c.p.s. to 25 Kc/s, 26 db gain. 
For use With valve or transistor equipment. 
Full instructions supplied. Brand new. 1 7/ A *'' 

Guaranteed. Details S.A.B. ■ */** 2, 



■M 



NEW TUBULAR ELECTROLYTICS 



CAN TYPES 
16-H6/500V 11 
50+50/350V 
60 + 100, 350V 
32 +38.250V 
32+32/450V 
32- 1 -32i-32/350v. 8/6 
100 + 60 + 50 3S0v.9 8 



wi- 
ll, 6 



m 



2/350V . . 2/6 I 100/26V . . £/ 

4 350V ..26 250 25V . . 2/6 

8/460V . 2 8 500 25V . . 4 - 

16/ 450V , . 3.'- S +8, '450V 3.8 

32450V .. 4/- 8 + 1B/450V |/- 

25/2SV .. B/- | 16 + 18/450V5- 

50 50V .. 2.'- | 32 + 32 ; 350V a - 

StJB-MIN. ELECTROLYTICS. 1, 2, 4. S. S, 18, 25, 30, BO, 100, 

200mF 15V 2'-: 500, lOOOmF 1BV 3,6; 2000mF 25V "-. 

CERAMIC. lpF to Q.OImF, 9d. Silver Mica 2 to SOOOpF, Bd. 

PAPER 350V-0 1 9d, 06 2/8; lmF 3/-; 2mF 150V 3/-, 

500V-0 001 to 05 Bd; 01 1/-: 25 1/6; 0-47 5/-. 

1.000V-0 001. 0022, 0047, 01, 02, 1,6; 047, 01, 2,6, 

SILVER MICA, Close tolerance 1",,. 2 2-500pF 1/6; 560- 

2,200pF 2.'-; 2,700-5, 600pF 4,-; 8.800pF-Q 01, mid 6/-; each. 

TWIN GANG. "0-0" 208pF + 176pF, 11/-; Slow motion 

drive 365pF+36SpF with 25pF + 25pF. 11-; SOOpF slow 

motion, standard 9-; small 3-far.s SOOpF 22-. SHORT 

WAVE. 25pF, 11-, 

CHROME TELESCOPIC AERIALS 23in. 5.,'-. 

TUNINS. Solid dielectric. lOOpF, 300 pF, SOOpF. 7,- each. 

TRIMMERS, Compression 30, 50. 70pF. 1.-; 

lOOpF, 150pF, 1 8: 2S0pP, 1 6: SOOpF. 750pF,2.-; 1000pF,2 6. 

RECTIFIERS CONTACT COOLED ball wave 60mA 7 6; 

86raA 9/6. SILICON BYZ13 6/-; BY10O 10/-, 

Full wave Bridge Rectifiers 75mA It'.'-; 150mA 19/6. 

EX-GOVT. RECTIFIERS 250v. 200mA 6/-. 

NEON PANEL INDICATORS 250v, AC, DC Red, Amber 4.-. 

RESISTORS. Preferred values, 10 ohms to 10 meg. 

i w., t w., 1 w., 20% 3d.; U w. Sd,; B w. 1/-; 5 w. 10% 6d. 

HIGH STABILITY. [ w. 2% 10 ohms to 10 meg., 2/-. 

Ditto 5%. Preferred values 10 ohms to 23 meg..Sd. 

WffiE-WOUND RESISTORS 5 wait, 10 watt, 15 watt, 

10 ohma to 100K, 2/- each: 2: watt. 1 ohm to 8 2 ohms. 2/- 

Q MAX CHASSIS CUTTER 

Complete: a die, a punch, an Allen screw and key 
iin, 16f6 iin. 17/6 liin, 19/6 lite. 24/- 2 /-in. 44 '3 
tin. 166 lin. 18/6 Hin. 20/6 liln. 29"- 25m, 67.3 
iin, 16/9 li'.in. 19/8 ljin. 21/6 2iJt. 39,9 lin, sq. 36,6 

TRANSISTOR MAINS POWER PACKS. FULL WAVE 
9 volt 500mA. Size 41 ■ Si K 2in, Metal caae. 7ft > 
Crackle finish. Output terminals. On/off switch. * **/ 
Half Wave 9 volt 50mA. Size 21 11, in. Snap terminals 36, - 



MAINS TRANSFORMERS 5 l°:U 

250-0-250 50 mA. 6.3 v. B amps, centre tapped 22/- 

250-0-250 80 mA. 6.3 v. 4 amp. 28/- 

250-0-250 80 mA, 6,3 v, 3.5 a. 6.3 v. 1 a, or 5 v. 2 a. 88/- 
350-0-350 80 mA. 8.8 v. 3.5 a. 8.3 v. 1 a, or 6 v. 2 a. 38(- 
300-0-300 v. 120 mA„ 6,3 v. 4 a, C,T. ; 6.3 v. 2 a. 60/- 
MINIATDRE 200 v. 80 mA„ 6,3 v. 1 a.21 - 2 ■ l;m. 15/- 
MIDGET 220 v, 45 mA„ 8.3 v. 2 a. 2; r- 2! 2in. . 18/- 

HEATER TRANS. 8.3 v. 15 a 10/6 

Ditto sapped sec. 1.4 v., 2. 3, 4, 5. 8.3 v. 11 amp. . . 16/8 
GENERAL PURPOSE LOW VOLTAGE. Outputs 3, 4, 5, 

6, 8. 9, 10, 12. 15, 18, £4 and 30 v. at 2 a - 38 - 

1 amp., 8, 8, 10, 12, 16, 18, 20, 24, 30, 36, 40. 48, 60. 38- 

AUTO TRANSFORMERS 0-116-23O v. Input/Output, 

60w. 18/6; 160w. 38.-; GOOw. £5: lODOw, £12. 

CHARGER TRANSFORMERS. Input 800 250 v 

lor 6 or IBv,, 11 amp., £4,'-; 4 amp., 38/-. 

FULL WAVE BRIDGE CHARGER RECTIFIERS : 

6 or 12v. outputs. 1J amp. B/-; 2amp.il/-; 4 amp. 17.'-, 



COAXIAL PLUG 1 3, PANEL SOCKETS 1.3, LINE 3 6. 
OUTLET BOXES. SURFACE OR FLUSH 5,'-. 
BALANCED TWIN FEEDERS 1- yd. 80 ohms or 300 ohms. 
JACK SOCKET Std. open-circuit 2 8, closed circuit 4/6; 
Chrome Lead Socket 7,6. Phono Plugs 1:-. Phono Socket 1;'-. 
JACK PLUGS Std. Chrome 3/-: 3 5 mm Chrome 2 6. DIN 
SOCKETS Chassis 3-pin 1 6: 5-pin 2 -. DIN S09KETS Lead 
3-pin 3,6: 5-pin 5 -. DIN PLUGS 3-iin 3/6; 6-pin 5;-. 
VALVE HOLDERS. Dd.; CERAMIC 1/-: CANS 1/-. 




E.M.I. 131 x 8in. 
LOUDSPEAKERS 



U.UU M'tniii:'. 

45/- 



With flared tweeter cone and ceramic 
magnet, 10 watts. 
Bass res. 45-80 cps. 
Flu* 10,000 kiuss. 
Stale 3 or 8 or 15 ohm. Post 2,'B 
Also with twin tweeters. With cross- 
over. State 3 or 8 or 15 ohm. £A 

Poat 2/6, *S* 

Recommended Teak Cabinet /C 
Size 16 ■■! 10 : Sin. Post 26 t3 



47/6 

Post 2/6 



"THE INSTANT" 
BULK TAPE 
ERASER AND 
RECORDING 
HEAD 
DEMAGNETISE!? 

200/250 v. A.C. Leaflet S.A. 

Minimum Post and Packing 2/6. RETURN OF POST DESPATCH. Hf-FI STOCKISTS. 

RADIO COMPONENT SPECIALISTS 

List /,'-. Written guarantee with every purchase. (Export: Remit cash and extra pottage 

816 




MINI-MODULE 
LOUDSPEAKER KIT 

10 WATT 65/- CARRIAGE 5- 

Triple speaker system combining on ready cnt baffle. 
'■ in. chipboard 15 in, . Siin. Separate Bass. Middle 
and Treble loudspeakers and crossover eondenser. The 
heavy dnty 5 in. Bass Wooler unit has a low resonance 
cone. The Mid-Range unit ia specially designed to add 
drive to tht middle register and the tweeter recreates the 
top end ol the musical apectrum. Total response 
20-15,000 cps. Full instructions lor 3 or S ohm. 
TEAK VENEERED BOOKSHELF ENCLOSURE. 
16 -'- 10 :. 9 in. Modern Scandinavian fr _ , , 
fluted Iront design tor Mini-Module. w rostJI _ 



ALL MODELS "BASER SPEAKERS'* IN STOCK 



BAKER 12in MAJOR £9 




30-1*,500 c.p.s., ISin 
double cone, wooler and 
tweeter cone together 
with a BAKER ceramic 
maicaet assembly having 
a fiux density of 14,000 
gauia and a total fin* ot 
145,000 Maxwells. Ban 
resonance 40 c.p.s. Rated 
20 watts. State 3 or g or 
15 ohm. Post Free. 



Module kit, 30-17,000 c.p.s. 
with tweeter, crossover, 
baffle and / I 1 I ft ft 
instructions. *•■ '• ■«•" 



BAKER *' SROOT SOUND " SPEAKERS 

' Group 25 ' 'Group 35' 

12in £-} lain XO 

s-/ -in _.» *•' 



25 watt 



35 watt 



■ 8 or 15 ohm, 

' Group 50' 

1 Sin / I Q 
50 watt *■'* 



TEAK HI-FI SPEAKER CABINETS. Fluttd wood Iront. 

For 10 or 12in round Londapeaker * f.0.0. 

For 13 ;: Sin or Sin ronnd Loudspeaker IB. 0.0. 

For 10 6iu or 8iin round Loudspeaker £4,0,0. 

LOUDSPEAKER CABINET WADDING ISin wide, 8 - tt 



TWO-WAY CROSSOVER NETWORK 300 o/S. With variable 
tweeter attenuator giving accurate high / low frenuency 
balance. Mounted on panel 5 'in. < 4in. with control knob, 
tweeter and woofer leads and input terminals, 38 - 

Suitable lor 3 to 8 ohm impedance. Post 2.'-. 
Horn Tweeten 2-16kc/s, 10W 8 ohm or 16 ohm 39/6. 
De Luxe Horn Tweeters 2-18 Kelt, 15W, 16 ohm 58/6. 
ELAC Moving Coil De Lnie Cone Tweeter 5 ohm S5..-. 
3000 c.p.s. CROSSOVERS 3 or 8 or 15 ohm IS/-. 
SPECIAL OFFER I 80 ohm. 2iin, Siin. dia.; 35 ohm, 3 in. 
25 ohm, 3in. dia.; 8 :< 4in; 8 3in; B Sin.i "T I ft EACH 
IB ohm, SSln. dis.; 7 4in; S >: 5ln. ■ '/° TYPE 

S ohm 6 - 4In; 3 ohm. 2 Jin, 3in, Sin. 6 ' Sin, 7 ' 4in. 
LOUDSPEAKERS P M 3 OHMS. 6lin 22 : 8; 8 5in, 25.-: 
8 y- 8! in IS,-: Bin 35.-; 10 ... Bin 38/-.' 
5 in . WOOFER, S watts max. 20-10,000 cps. 8 or 15 ohm . 38, -. 
ELAC S in. De Luxe Ceramic 3 ohm or 15 ohm 50,-. 
SPECIAL OFFER I FAMOUS RICHARD ALLAN LOUD- 
SPEAKERS 8 or 10 or ISin Twin cone 3 or 15 onm 30,6. 
OUTPUT TRANS. EL84 etc. 5 : MIKE TRANS. 50:1 5 . 
SPEAKER COVERING MATERIALS. Samples Large S.A.E 



SOUND ACTIVATED 

PSYCHEDELIC 

LIGHT BOX 

Fascinating light patterns ot 
Green, Blue, Red and Amber. 

Works with any mono or stereo 
amplifier, or radio output. 
Input required 0.2 watts. 
A.C. mains operated. Size 13 
X 13 4in. 

£ I 2. 1 0.0 Fost Free 




ALL EAGLE PRODUCTS 

SUPPLIED AT LOWEST PRICES. 
ILLUST RATED EAGLE CATALOGUE 5/ ■■ Post free. 

BARGAIN AM TUNER. Medium Wave. I A 

Transistnr Sunerhet. Ferrite aerial. 9 volt. 



BARGAIN 4 CHANNEL TRANSISTOR MIXER. 
Add mnsical highlights and sound effects to recordings. 
Will mix Microphone, records, tape and tuner 
with separate controls into single output. 8 vnlt. 



£3 

9 volt. 

£10 



BARGAIN FM TUNER 8S-10S Mc/s Six Transistor. 

Printed Circuit. Calibrated slide dial tuning. 

Walnut Cabinet. Size " ■ 5 4in. 

BARGAIN FM TUNER as above. £J 10 

less cabinet. I "" w,v 

FMSTEREOMULTD?LEXADAPTORIoraboveorOO/A 

general us e. Ready made with 4 transistors. 6 diod es »*/»* 

BARGAIN 3 WATT AMPLD?IER. 4 Transistor AO/|t 
Pusn-Pnll Ready built, with volume control. Bv. *** / ** 



ic RADIO BOOKS * (Postage 9d.) 

Practical Radio Inside Out 

Practical Stereo Handbook 

Supersensitive Transistor Pocket Radio 

Radio Valve Guide, Books 1, 2, 3, or 4 ea. 5.- No. 5 

T.V, Fault Finding 405/625 lines 

Transistor Communication Sets 

Wireless World Radio Valve Datn , 

Transistnr Circuits lor Radio Controlled Models 

Valves, Transistors and Diodes equivalents Manual. 

Coil Design and Construction 

Hartley on Hi-Fi Radio Tuners 

22CircnitsIorMicro-AlloyTransistors 

Practical Car Radio Installation 



... 4/6 
... 3/6 

... 3/6 
ea. 6/- 
... 8/6 

.,, 6/- 
.10/- 
... 7/6 

. 10 6 
... «/- 
... 5/- 

... 6/- 
... 6;'- 



3 inch MOVING COIL METERS BRITISH MADE 

Various calibrations/movements. 500 Microamp; 77 If. 
1 Milliamp ; 50-0-50 Microamp. et c. S.A.E. l or list. ■* ' I v 

BALFOUR MAINS ELECTRIC 
MOTORS. (120v. or240v. AC). Six* 
81 X at x Hin. Clockwise 1,200 r.p.ra. 4 
pole 50mA, Spindle I .: 3/20, 17 A 
Post 2/6. "/ w 
E.M.I. TAPE MOTOR. 120v.or240v. 




AC. Heavy duty 1,200 r.p.m, 4 poh TCI. 
135mA (M illustrated ). Post 2/8. iJ / 

CUSTOMERS FREE CAR PARK, CALLERS WELCOME. 

337 WHITEHORSE ROAD, CROYDON 

Open 9-6 p.m. (Wednesday* 9-1 p.m., Saturdays 9-5 p.m.) 

) Buses 133, 68 pass door. S.R. Stn. Selhunt. Tel. 01-884-ttjfiS 
Practical Electronics October 1970 




and component layout details. Here, mounting strips 
with ceramic stand-offs are used to carry the majority 
of components, with the remainder supported by the 
switch, control potentiometer and meter terminals. 

When ordering the triac the heat sink should be in- 
cluded. The latter is soldered to the long tag strip 
terminals, then the triac is clipped in. A view 
of the heat sink mounted triac is given in Fig. 3. 

In view of the light loading of the triac — less than 1A 
— the use of a heat sink as such is not really called for, 
but it does provide a convenient way of mounting. 

If a double-pole change-over switch is available, it is 
worth while to make use of the second pole as in Fig. 4 
to bring in a neon indicator. 

The neon will light when the enlarger lamp has full, 
uncontrolled, power applied to it, and acts as a warning 
to the photographer that this is so. The inadvertent 
use of this setting for exposing, giving over-exposure 
of the print, should thus be avoided. 

USING THE CONTROLLER 

The output of the controller is adjusted as required 
so that a constant meter reading is obtained; the 
reading chosen must, of course, be a little lower than 
that given by the lowest mains voltage likely to be 
encountered. 

The switch SI can be used to apply the full voltage 
to the lamp for the purpose of focusing. 

The numbered curves A and B in Fig. 5 indicate 
light output from a 75 watt enlarger lamp with: 

(a) Variation of applied voltage, that is, without the 
controller. 

(b) Variation of mains voltage but with a constant 
meter reading setting of 0-6mA. 

Graph (c) Uncontrolled meter reading with changing 
mains voltage. 



The output of the lamp in the lower graph is expressed 
in terms of the reading on a Weston- 3 exposure meter. 
It can be seen that the change of almost 1^ stops, given 
by an uncontrolled lamp when the mains changes from 
250 volts to 200 volts, can be reduced to zero by this 
controller, so giving good correction for both black 
and white and colour photography. -^ 



Meter 
reading 
(mA) 




Weston 
reading 



25 

13 














£.] 


























rj 




















90 2 


X) 2 


tO 2 
Mains k 


20 2 
Itagt 


JO 2 


40 2' 






tV z «ops 



Fig. 5. Graphs showing fight output from T5W 
enlarger lamp with; (a) Variation of applied 
voltage, (b) variation of mains voltage with constant 
meter reading of 0.6mA, (c) Uncontrolled meter 
reading with changing mains voltage 



Practical Electronics October 1970 



817 




OF LOGIC IC'S 



PART FOUR— By R. W. COLES 

PRACTICAL DTL— 

SLIDE PROJECTOR DELAY TIMER 

Diode transistor logic is available in all of the 
three package outlines commonly used to house 
integrated circuits, namely the modified TO-5 can, the 
miniature flat-pack, and the most popular of all, the 
14-pin dual in-line plastic package. The dual in-line 
package is recommended to amateurs because of its 
cheapness and comparative simplicity in use. 

It might be thought that "breadboarding ,, is a thing 
of the past with such sophisticated circuits as these, 
but this is far from true. With logic i.cs it is a simple 
matter to "breadboard" complete systems instead of 
just individual circuit blocks. These ready made 
blocks are just as robust as transistors, and in many 
respects they are more so. 

Home designed printed circuit boards are still useful 
for the finished article, although the layout design will 
take much longer. It is very difficult to remove a 
package with so many pins once it has been soldered to 
such a board, 

IX. BREADBOARDING 

One breadboarding system that can be used with 
success, enabling easy removal of the integrated circuit 
package, employs plain white stiff cardboard, which is 
obtainable from most stationers very cheaply. 

The package layout is first decided upon, and then 
roughly sketched out on the board, holes are then made 
in the board to correspond with the i.e. lead-outs. 
There is no need for accurate marking out; an i.e. can 
be used directly as a guide. These holes can be made 
simply with dividers or the point of a pair of compasses. 
If they are made to take the lead-out tags tightly, there 
will be no need to anchor the packages to the board. 

All that remains is to wire up the circuit as required. 
The wiring can be drawn on the board before assembly, 
but remember, manufacturer's diagrams of i.e. pin 
connections, unlike those of valves, assume you are 
looking down on the top of the package. 



By this time you may be asking yourself just what 
you can build with i.e. DTL circuitry. Of course you 
would like to build your own computer, but it could be 
far too expensive. 

There are vast new areas open to the experimenter 
working with just a handful of gates and flip-flops. 
Examples are logic control of a model railway system ; 
an automatic dipping headlight system for a car, 
which provides a manual back-up and manual over- 
ride. Automatic indication of an approaching car 
when in the manual state can be included, with a 
warning signal when you have overridden the automatic 
system. Perhaps you might like to try digital control 
of a model aircraft. Another idea is a digital clock 
with a display on numeral indicators. This article 
concerns itself with one application — a slide projector 
delay timer. 

SLIDE PROJECTOR DELAY TIMER 

This simple design, which employs DTL integrated 
circuits, is intended to be used in conjunction with an 
automatic slide projector, and allows such a projector 
to run continuously and unattended, changing slides 
roughly every ten seconds. It is mainly intended for 
use with a circular slide magazine containing 100 slides 
which, in the case of the prototype, was fitted to a 
Gnome projector with remote slide changing capability. 

The main use of such an installation is as a visual 
demonstration aid at exhibitions (the original set-up 
was used to simulate a radar display) the projector 
being behind an imitation radar console. 

An automatic slide projector of this type changes 
slides when a remote control button is pressed twice, 
the first press causes the slide carrier, containing the 
slide, to move to the open position, and also rotates 
the magazine one position. The second press allows 
the carrier to return to the display state with the new 
slide. 

If instead of pressing the button twice, it is kept 
depressed after the first press, the above process con- 
tinues indefinitely, with the disadvantage that whereas 
it takes about two to three seconds to change a slide, 
the time during which the slide is projected only 
amounts to about half a second. This situation is 
clearly unsatisfactory for the continuous display 
sequence, as it results in only a brief display every two to 
three seconds. 

Experiments with the button show that a press of 1$ 
seconds was sufficient to produce a complete change of 
slide, a shorter press resulted in only half a change, and 
a longer press caused the mechanism to commence a 
second change. A suitable interval between changes 
was decided on as about ten seconds. 

PULSE FREQUENCY DIVISION 

In this particular application the requirement was 
to design a timer which closed a pair of relay contacts, 
wired in parallel with the change button, for li 
seconds in every ten. The eventual design utilises a 
pulse generator to provide one pulse every 1£ seconds. 
The output of this generator is divided by eight in a 
binary counter. 

As each of the counter's eight states lasts for li 
seconds, and occurs once in every ten (8 x 1-j), it is 
a simple matter to decode one of these states and use the 
resultant output to operate a relay. 

The circuit used is shown in Fig. 4.1a, and contains 
three bistable i.e. packages type 9945, and one triple 
3-input gate package type 9962; the pin connections 



818 



Practical Electronics October 1970 



MOTORS 



HIGH PRECISION MAINS MOTOR 

230V 60 Hz i h,p. continuously rated, 
3,000 r.p.m. Made by Croydon Engineer- 
ing Model KA 00 JFB, Suitable lor 
capstan motor. Size 81a long, 4) in dia- 
meter b i th Sin diameter flange and 4 filing 
holes. These motors are Capacitor Start, 
Capacitor Bun, supplied lees Capacitor. 
Also available 3 Phase. J4.10.O. each. 
£1.5.0. P. &P. 



SHADED POLE MOTORS 120V 50Hz 

Precision made as used in record decks and 
tape recorders. Suitable many other 
applications. 10/- each. P. # P. 3/-. 



PRECISION MOTORS by PULLIN 
28V, 3,000 r.p.m., 0-0018 h.p.; 28V, 
5,000 r.p.m., 00014 h.p.; each «.I0.0. 
P. * P. S/-. 



HYSTERESIS REVERSIBLE MOTOR 
Incorporating two coils. Each coil when 
energised will produce opposite rotation ot 
output shaft. 120V MHz, 1/10 r.p.m. 80/- 
each. P. & P. 3/-. 



LOW TORQUE HYSTERESIS 
MOTOR MA23 

Ideal for instrument 
chart drives. Extreme- 
ly quiet, useful Id 
areas where ambient 
ooise levels are low. 
High starting torque 
enables relative high inertfa roads to be 
driven up to Ooz/ln. Available in the 
following speeds and ranges: 240V 50Hz, 
4 r.p.m., 2 r.p.m.. If r.p.m., 1 r.p.m., 
f r.p.m., i r.p.m., j r.p.m., i r.p.m., 
1/10 r.p.m., 1/12 r.p.m., 1/20 r.p.m., 
J/4B r.p.m., 1/80 r.p.m., 1/300 r.p.m. 
Hf/~ each. P. & p. 3/-, 





HYSTERESIS CLUTCH MOTOR 

With integral elutph allow- 
ing the motor to drop out 
of engagement with the 
gear train, thereby facilitat- 
ing easy resetting when 
used in timers or In con. 
junction with a light spring. 6 oz torque at 
240V 60Hz, 1/12 r.p.m., t r.p.m., 
i r.p.m., i r.p.m., } r.p.m., IS r.p.m. 
120V 50Hz, 1/12 r.p.m., 1/10 r.p.m., 
i r.p.m., 5/12 r.p.m., 4/11 r.p.m., 2 
r.p.m. 120V 80Hz, i r.p.m,, 1 r.p.m. 
21V 50Hz, 1/20 r.p.m., 4 r.p.m. 85/- each. 
P. * P. 3/-. 



O.C, MOTORS 

Similar to above type MD 83. 28V 
1/20 r.p.m., 1/80 r.p.m., 1 r.p.m. 12V 
1/20 r.p.m. 24V 1/15 r.p.m. 30V 
l/12r.p.m. t0/-. P.4P.3/-, 



SYNCHRONOUS MOTORS 

200/250V 60Hz. Mew conditio**, ex-equip- 
ment, S.7 1 r.p.h, and 1 r.p.m. Self 
starting, complete with gearing shaft gin 
dia., Jin long. 80/-, P. £ P. 3/-. 




OSCILLOSCOPE TYPE CT S2 
A very handy minia- 
ture portable instru- 
ment for general 
purpose applica- 
tions. 2}in dlam. 
tube. Wave form 
Investigation from 
10Hz-2OMMz. Pulse 

monitoring duration 50 microseconds to 0-1 
microsecond. Time base tree running 
10Hz-40kHz. Also single sweep facility 
from 50 microseconds to 3 microseconds. 
"V" Amplifier. Delay Line Calibration 
Voltage. Power supply 1 10-25OV 40/60tts. 
SOW. Supplied with metal carrying ease. 
L. 13in. H. Bin. W. 5iin, Weight 14 J lb. 
Price tSti. P. & P. 30/-. 



AVO TRANSISTOR ANALYSER CT 446 

In V. G. condition. Current instrument. 
Battery powered. Size 15J" >: SI* x 5". 
Weight 151b. Price M2.10.0. Carr. £1. 



ELECTRIC CLOCK MOTOR 

NEW 200-250V, 50Hz, 2W. Synchronous 
Induction motor. 2 revs, per hour. O/P 
shaft. Jin dia v. |!n long. Clockwise 
rotation. Three-holed mounting at 120 J 
on 2in PCD. Price IS/-. P. & P. 6/-. 



LOW COST ELECTRONIC & SCIENTIFIC 
EQUIPMENT AND COMPONENTS 



DELAY LINE 

2 microsecond, 4,000 ohm. Tvpe MOX 
2484D. Length 2Jtn k fin x |in. En- 
capsulated module. Price 80/-. P. & P. 5/-. 



STOCK CLEARANCE 

In order to give clearance In our new 
stores the following scientific equipment 
Is being sold at realistic prices. All items 
are offered in "As is condition". 

L.C.K. Bridge B121 

Wayne Kerr £12 .10, 

L.C.K. Bridge XJB202 

BLP *1S.10.0 

L.C.K. Bridge D197A 

Muirhead £7.10.0 

Crystal Calibrator. . . TF723A 

Marconi £16. 0.0 

Counter — 1 Digit SA20 

Eacal B9.10.0 

Counter^S Digit SA43B/10 

Kaesl £11.10.0 

Freq. Meter BC-22-IM 

Bendix £3. 10.0 

Freq. Meter 7I4A 

Dawes £4 0. 

Multimeter AC/DC E772 

S. Weston £8.10.0 

Safely Ohnietor 12MA 

Evershed k. Vignolea .... £5. 0. 
Bridge Oscillator 703 

Airmec £5. 0.0 

L.P. Oscillator, O420 

Dawes £7, lo.o 



MINIATURE 
UNISELECTORS 

3 bank, 12 way, 250 ohm, 
24V. Type 220OA. Sup- 
plied complete with plug-in 
base. Size Sin x lin x 2in. 
A very neat precision com- 
ponent. Price 14.18.6. 
P. A P. 5/-. 




AVOMETERS 

These well-known portable test instru- 
ments have been overhauled and are 
offered complete with leads, crocodile 
clips and prods. 

Model 9 SX . . £24.10.0 
Model 8 . . £18. 0.0 

Model 7 .. £14.10.0 

Model 7 Mk.H £15. 0.0 
Model 7X .. £15.10.0 
Model 4S A .. £11. 0.0 
Model 47A . . £10. 0.0 
Model 40 . . £10. 0.0 

Model 48 A complete with voltage multi- 
plier for 480V and 3600V. Current shunts 
for 120 A and 480A. A.C. Current trans- 
former tor 20 A and 80A. In special 
■wooden box. £14.10.0. P. 4 P. 15/-. 





i^r-jr 



SET OF MEASURING INSTRUMENTS 

Brand new 
high grade 
moving coil 
meters. Ideal 
auto- elec- 
trics and 
other general 
d.c. appli- 
cations. Supplied with 3 shunts in neat 
attache type metal carrying case. Speci- 
fications: Voltmeter 0-1 5V, 0-150V, 
0-4MV. D.C. Linear mirror scale 3mA 
F8D. Ammeter unahunted T'SniA FSD. 
Used with 3 shunts to give ranges of 
0-0-3A, O-0-75A, 0-1-5A, 0-7-6A, 0-15A, 
0-30A. The ammeter can also be used as u 
0-75 mV Voltmeter. Scale length 83 mm. 
Accuracy 1%. Case moulded plastic. 
Meter size 4]ln X ijin. List price £30. 
Our price £5.19.8. P. & P. 30/-. 



PORTABLE WHEATSTONE BRIDGE 

Specification. Type: Moving Coil Galvano- 
meter, Ranges: 1. 05 to 5 ohms. 
2. 0-5 to 50 ohms. 3. 5 to 500 ohms. 
4. 60 to 6,000 ohniB. 0. 500 to 50,000 ohms. 
Scales: Switched. Slidewirc: 05 to 50, 
Galvanometer Scale: 10-0-10. Case: 
Moulded plastic. Interna] Source: 4V 
Dry battery. Dimensions: 200 X J 10 ^ 
85mm. Weight; 9kg. List price £25. 
Our price £9.19.6. 



OSCILLOSCOPES 



Cossor 103S 

Cnssor 1049 , , , , 
Bolartron 523 . . 
Solartron D300 . . 
Furzehill 0100 , . 
FurzehlllOlIO .. 
Furzehill 1 0*411 
Airmec 249 
Airmec 723 , ... 
Carriage estra. 



£19.10.0 

£25. 0.0 
£49.10.0 
£20. 0.0 
£19.10.0 
£19.10 
£19.10.0 
£15. 0.0 
£15. 0.0 



COUNTERS 



ELECTRO MAGNETIC 
COUNTER 300 ohm 24V. 
Slow impulse counter 
of 10 impulses per 
second. 8/6. P. & P. 3/- 




6 DIGIT ELECTRICAL IMPULSE 
COUNTER with electrical and mechanical 
reset counter driven by 1 10 V DC 4400 

ohms coil. Reset 110 V DC 800 ohms coil. 
Housed in plastic-alloy case. The units can 
be Interlocked with each other to give 
vertical or horizontal displays. Price 59/8. 
P. A P. 5/-. 



VEEDER ROOT 6 DIGIT COUNTER 

Suitable for counting all kinds at pro- 
duction runs, business machine operation. 
Mechanically drl ven . Beset type KA 1337 , 
manual knob. Ex-equipt, but new con- 
dition. Special price 25/- plus 6/- P. & P. 



3 DIGIT RESETTABLE COUNTER 
Totalising 48V d.c. at. 48mA ; 10 impulses/ 
see. Length 4tn :< Jia :-. ]j n . Price 
£3.15.0. P. A P. 5/-. 



4 DIGIT NON-RESETTABLE COUNTER 

Totalising 10 Impulses per second. Length 
3iin x ljln >: ljin. 24V d.c, 300 ob:a. 
Price 6/6. P. & P. 6<-. 



6 DIGIT RESETTABLE COUNTER 
Totalising 240V SflHz. Viewing wmdnw 
•Jin X Jin. Ex- equipment. Price 65/ -. 

i 1 . a r. j.. 1 -. 



6 DIGIT TOTALISING NON-RESETTABLE 

COUNTER 

Mechanical operation. Chromium finish. 

Length 1 I in X lin :: lin with viewing 

window iln X A In. Ex-equlpment. Price 

8/8. P. A P. 2/0. 



BERKELEY DECIMAL COUNTING 
UNIT 0-9 

4 valves double triode 
type 5985 sped n I quality 
Unit plugs into standard 
octal base. Modular con- 
struction with 10 minia- 
ture neon lamps oudisplay 
panel. Power supplies 
S'3V, a.e., 150V i.e. Cut- 
<>n or Cat -off — 15V. Size 
5|in x biiax jin. Price 
68/-. P. & P. 5/-. 




MINIATURE DIGITAL DISPLAY 

Operates on a rear 
projection 6-3V. 
pilot lamp. Charac- 
ter afio J* high. 0-9 
digits with degree 
symbol, i.e. {4 1 ). 
Dimensions 1* wide, 
31" deep, 1 A " high. 
List price 6 gne. Our 
price 40/6. P. & P. 




EAC DIGIVISOR Mk. II DIGITAL 
READ-OUT DISPLAY 

Uses a sensitive moving 
coil movement to project 
digits 0-9 on to a viewing* 
screen via an optical lens 
system. Image height J'. 
Lamp r,-3V. Sensitivity 
250 micro-amp. Dimen- 
sions L. 4,*". W. Jj". 
H. It". Price £3.10.0. 
P. & P. o/-. 




SOLENOIDS 

High quality solidly constructed solenoids. 
Actuated by 48V 300 O coll. Overall length 
3" ;■: 1' square with a i" travel ot the l" 
dia. shaft. 8.8. P. & P. 3,'-. 
24V. 70 ohm. Armature i" movement. 
Lug type ntlliig. L. 1J* x J' k J". 
Price *;8. P. & P. 2/8. 



LAMPS 

260V, 15W, MBC. Panel lamps. Ideal 
making up displays, etc, Length 2 J in :c 
liln dia. Special offer, 10 lor £1, P. & P. 

SI— 



MEMORY CORE STORES 

42 x 52 2K bit ferrite core store complete 
with 84 OA 10 Inatl diodes. Ideal (or build- 
ing computer store or holding information 
In binary form. Price 55/-, P. & P. 7/li. 



MINIATURE MOVING COIL 

RELAY SI 15 
AtUfjJI fc. 87 Sangamo Weston, 
• • * ^ suitable for D.C circnit. 
A high sensitivity relay 
more sensitive than the 
electromagnetic type. 
Single Coll ReeiEUiii.-w 
310 micro amps. 315(). 
List price £4. 10. Our price 80/-. P. &P.S/-, 



o 



NUMICATORS 



Fig. size 16mm. 
Cold cathode gas filled In 
line 0-B digital display 
tubes. Long fife expect- 
ancy. Minimum striking 
voltage 180V. Side reading 
Type XN 13 and XX 3, 
amber. Price 18/8 each. 
P. 4 P. 2/6. 



DOUBLE AUDIO FADERS 

These hard to get, pro- 

%fessional recording studio 
units are ideal for audio 
signal mixing, lading pro- 
grammes In and out, etc. 
Two bank 1,000 4- 1,000 
ohm wire-wound parallel 
connection to give 500 ohm 
1W, Independent tracks fitted scale 
makings, with red and blue control knobs. 
Panel mounting. JBx -equipment. Price 
£3.19.6. P. & P. 7/6. 



CARRIAGE EXTRA 



LINEAR THYRISTOR CONTROLLED 
LIGHT DIMMER— BRAND NEW 

High grade full wave 

bridge circuit gives, 

linear control of 

light brightness. Ideal 

for controlling room 

lighting and a.c./d.c. 

cqnunutator motors 

fitted to portable 

electric hand drills. Kits Btaudnrd 21u 

conduit box. 240V, 50Hz, tiOOW. Price 

58/fl. P. & P. 2/6. 




POCKET CALCULATOR 

Save time and solve all 
your multi|iHe:iUon, divi- 
sion, percentage, cube 
and square root problems. 
Easy to use pocket calcu- 
lator with no errors. In- 
valuable dally aid, 
should last a lifetime, 
offered complete in black 
wallet with full Instruc- 
tions, 3 fin dlain, 126 
each, P. & P. 1/6. 




RAPID HEAT SOURCE . 



ite 



from hi and new Xnhi Red Tubular 
Quartz Lamps. Ideally suited as heat 
source for Drying Ovens, Egg Hatching, 
Incubators, etc. 240V, f,440V, 20,000 
Angstroms. Length 12iu : lin dia. 
Price 15,'-. P. &. P. o/-. 




REPEAT CYCLE TIMERS 

These timers repeat a set 
cycle of switching opera- 
lions via a cam and 
micro switch, for as long 
as the motor Is energised. 
Single Cam £B 21iu 

2 miu, 4 mtn, 5 nun, 
6 min cycles at 45/-. Twin Cam P.D 22 in 

3 min, 4 min cycles at 66/-. 4 Cam RD 
24 in 4 min and 5 min cycles at 75;-- 3 
Cam BD 55 2 min 80/-. 6 Cam ED 20 in 
3 min, 4 min cycles at 65'-. 8 Cam BD 
281n 3 min, 4 mm cycles at 115/-. All plus 
P. & P. 6/-. 




ELECTRONIC BROKERS LTD. (Dep t. P.E.), 49-53 Pancras Rd., London, M.W.I Tel. 01437 7781-2 Cables: Selelectro 

Ix^l^HUMMiil^Hi^i^i^i^i^i^iMI^I^I^I^I^IMi' Open Mon.-Fri, p,m.|^|^HHiil^HI^I^HBI^I^I^I^I^I^I^I^a 



Practical Electronics • October 1970 



819 



IT SURPRISED US! 

We are probably South-East London's 
LARGEST COMPONENTS SHOP 



— but the other day a chap walked into our place at Deptford Broadway and said that 
he had only just found out that we were there. 

"What!" we said, "After 25 years? Incredible!" 

And then it occurred to us that there just might be other unfortunate electronics 
addicts who didn't know that there was a wealth of components close at hand. 

So to celebrate our Silver Jubilee let's tell them now . . . 



OPEN DAILY 
9.15 a.m. -6 p.m. 
/ Closed all day \ 
\ Thursday / 



TELEPHONE 
01-692 4412 



Garland Bros. Ltd. -- 

DEPTFORD BROADWAY (Corner of BrookmM Road) 

LONDON, S.E.8 



A LONG COOL LIFE 

for your valuable components with the 

S.D.C. DeC range of SOLDERLESS breadboards 



S-DeC 



T-DeC 



-DeC 



Available as single packs with accessories and 
control panel (d 29/6d or the DeCSTOR double 
pack containing 2 S-DeCs, accessories, control 
panel, all in a plastic storage container. Only 67/6d. 
A 4 DeC pack is available, only 117/6d. 

Now available to the amateur. 208 connection points. 
38indepertdentjunctions. Accommodates I.Cs using 
standard carriers. Three times the capability for only 
twice the price ! Unit pack with control panel 50/-d. 




Primarily for use with integrated circuits; further J 
details on request. 



T-DeC 



G?A 



T-DeCs, S~DeCs and Accessories are a!! obtainable [ 

from leading suppliers throughout the U.K. I 

In case of difficulty complete the coupon and i 

- / enclose POfCheque/Money Order value £ / / d 
mail without delay. Post to: J Money refunded if not satisfied, 



I Please send me : 

T-DeC Pack S-DeC Single Pack 

DeCSTOR Pack 4-DeC Pack 

Tick here if you requirefurtherdetails ofthe/±-DeC 




t 



S.D.C. Electronics (Sales) Ltd., ] Name 

34, Arkwright, Astmoor Industrial Estate, 
Runcorn, Cheshire. Tel.: Runcorn 5041 



820 



■ Address J 

Practical Electronics October 1970 




r. 1 



+12Vto1SV 



J&"1 



1 




DECODING? & 
GATE V^ ez 



TR5. 




czjHl] 

01 S5 OUTPUT 



INVERTER 
GATE 



470A 



2N697 



RELAY 
DRIVER 



Fig. 4.1a, Block diagram of integrated circuits with the additional discreet components required to make up the 
delay timer for a slide projector. VRI is adjusted so that the projector just goes through one slide change for each 
typ^^TCiiTp or AMC945 fj f'offf °™ C ° nt ° /ned /n 0ne '**" *>«*«*• «/!» w «. M" 1 or MIC962, the billables are 



Rtloj 



\ 



A 


& 


C 


■ Q 








1 


D 








t 
t 








I 






1 





1 


t 











1 










etc 





ON/OFF 



Rtcyeks 




Fig. 4.1b (left), 
counter states 



Truth table for the 



Fig. 4.1c (right). Suggested arrange- 
ment for supplying the d.c. power 



J-GNO TC] 




W5(S6S) 



9962(S6S) 






Fig. 4.2. Diagram of integrated circuit dual in-line 
outlines with arrangements of pin connections 
looking down on the top 



'Practical Electronics October 1970 




for these are given in Fig, 4.2. In addition three 
discrete transistors are used in the clock generator and 
relay driver circuitry, together with five resistors and 
two capacitors. 

The pulse circuit, which generates a negative going, 
steep-sided pulse every \\ seconds is ideally suited for 
this application as it uses few components, has a very 
high input impedance due to the complementary pair 
of transistors being used as a four layer diode, and 
produces a short output pulse with transition times of 
short duration. The time between pulses is set bv the 
CR time of Rl and CI. 

The capacitor charges through the resistor until the 
emitter of the transistor TR1 reaches a potential more 
positive than its base, which is set to a reference voltage 
adjusted by VRI . As soon as its base-emitter junction 
is forward biased in this way, it conducts sharply, and 
in turn causes the npn transistor TR2 to turn on. 

This process is regenerative; the capacitor is dis- 
charged through these two transistors which effectively 
short it to earth. When it has discharged TR1 is no 
longer forward biased, so it turns off and presents a 
high impedance to the CR network, which allows the 
capacitor to begin charging slowly again. 

The output pulse is taken from the wiper of VRI, 
which rests at the reference potential of about three 
volts until TR2 saturates; then it drops to about 200m V 
to form the pulse. 

This output is passed through one of the gates in the 
package, which speeds up its already fast edges and 
acts as a buffer to raise the pulse amplitude and current 
drive capability (i.e. fan-out). It also inverts the pulse. 

DECODING 

The flip-flops used in the 3-bit ripple counter are of 
the d.c. coupled set/reset type, andYequire two external 
feedback connections to enable their outputs to change 
state after the application of a negative going edge to 
their clock input terminal. 



821 



+ 8to10V 




2NM7 



'100 



fwiOl small hurt 1 



:ht?7 






soon 



ScttoSV 
+ 0.Z5Votv 

load 



prntt 



Fig. 4.3. Simple voltage regulator for connection 
between 9¥ d.c. power supply and the SV power line 
of the i.e.*. A 25/^F capacitor should be connected 
across the 5 V output 



Output A is connected to clock B input and so on, 
each stage dividing the clock frequency by two. Flip- 
flop C is up for four input pulses and down for four 
input pulses; after eight such pulses the counter ends 
up at the first state of 000. 

The correct interval between relay operations is 
obtained by decoding one of these eight states in one 
of the three input gates (G2). 

The H second pulse at the output of this gate drives 
the relay via the third gate, which is used simply as an 
inverter, and a relay driving stage TR3. 

The actual state of the counter which is decoded is 
immaterial, as they all must last for \\ seconds, and be 
separated by ten seconds. The state 000 is shown 
decoded in Fig. 4.1b. To decode any other state, 
it is necessary to feed to the logic gate the three counter 
outputs which are at a logic "1" state_at that time. 

Thus to decode 101 the outputs A B C are fed to the 
gate inputs. This last point is mentioned because it 
would be quite possible to decode more than one state 
and use this extra output (or outputs) to initiate other 
actions. For instance, a tape recorder could be 
started up by the counter state after that which changed 
the slide, perhaps giving a short commentary on the 
picture being displayed. 

POWER SUPPLY 

The power supply poses a slight problem, as the 5V 
required by the i.c.s is not available from dry batteries 
directly, and a simple mains supply without regulation 
is unlikely to be accurate enough. The prototype was 
run from a 4-5V battery with no noticeable ill-effects. 

The best solution is to use a higher voltage from either 
a power supply or batteries and trim this to exactly 5V 
with a Zener diode emitter follower regulator, a suit- 
able circuit being shown in Fig. 4.3. The supply to the 
relay circuit does not need to be accurately set and can 
be between 12 and 15 volts derived from batteries or a 
mains fed power supply. 

Next month: Part 5 will study transistor 
transistor logic (TTL) in which multi-emitter 
element transistors are incorporated in the i.e. 
package. The application of TTL to designing a 
binary adder will follow in Part 6. 



NEWS BRIEFS 



Manchester and Southampton Exhibitions Full 

Stand space at both of the professional electronic 
instrument shows sponsored by the Electronic 
Promotion Group, one at Manchester and the other at 
Southampton in September, are filled to capacity, claim the 
organisers. 

There are 37 exhibitors at the Electronic Instruments 
Exhibition at the Hotel Piccadilly, Manchester, from 
September 15 to 17. This is the fourth and biggest of the 
Manchester series. 

The Southampton show, with 27 exhibitors at the Sky- 
way Hotel from September 22 to 24, is also completely full 
up. This is the first EPG-backed exhibition in southern 
England and is part of the EPG policy of picking a new 
centre each year. Last year, in addition to the Manchester 
show, a similar exhibition was held in Coventry. 

Collision Course Solution 

A solution to air traffic jams and a method of drastically 
reducing the possibility of mid-air collisions through 
u*e of the fastest computer system ever developed has just been 
unveiled in U.S.A. Called the Staran IV system it has 
been developed by Goodyear Aerospace Corporation of 
Akron, Ohio, and can perform more than 40-million 
mathematical operations per second in predicting which 
planes are on collision courses and determining evasive 
action. 

One feature of the system is its ability to single out planes 
on collision courses and show them to air traffic controllers 
on a viewing screen as if they were the only planes in the 
air. 

Use of the Staran IV has been proposed to the U.S. 
Federal Aviation Administration who are analysing the 
system and considering its possible installation at U.S. 
airports. 

Thames Navigation Improvements 

Decca Radar have received an order from The Port of 
London Authority for replacement of the existing 
Thames Navigation Service Stage Two, which is the 
Gravesend to Cliffe section, to be completed in 1971. 

Existing fixed coil displays designed in the 50's will be 
replaced by the latest Decca equipment incorporating 
Deccaspot. With a 25ft scanner, two 25kW transceivers, 
three 1 6in displays, a Ferranti micro- wave link, and Cossor 
u.h.f. radio, the system will be identical to that of the 
Crayfordness-Broadness section. 

Deccaspot will be used for channel marking and for 
showing the designated anchorages recently published on 
Admiralty charts. This is a new system of very accurately 
positioned electronic spot markers, permanently displayed 
on the p.p.i. 



Flying Darkroom Transmitters 






The first half of a $8 million contract worth $4,172,500 
has just been awarded to the Goodyear Aerospace 
Corporation (GAC) of Akron, Ohio, U.S.A. by the U.S. 
Air Force. . , 

The contract is for 70 completely equipped, air mobile 
laboratories for processing and interpreting aerial 
reconnaissance film. , 

Included will be "data link" electronic equipment which 
can receive signals from reconnaissance aircraft and display 
in a matter of minutes, the terrain being covered. Thus, 
it is no longer necessary for reconnaissance aircraft to land 
and have film processed before intelligence officers can see 
what data is being gathered. 



822 



Practical Electronics October 1970 



§^■■1 


VUDi 




E.M.I. LOUDSPEAKERS 

MODEL 430. 131iu:8ln 
elliptical with twintwee. 
tcr*. 8 oh] n Impedance. 
10W. Brand new, guaran- 

t , ■ . ■ . I . L ind - A i : F r Ice 8 9 II . 

f. i p. 4/e. 

MODEL 150. I.'il-n si i. 
elliptical. 3 ami lo ohm 
impedance. 10W. Liud- 
Ai* Price 59.fi. P.&P.4/H. 
TEAK PIHIBH KFBA- 
KKR CABINETS. 
Size 18m : Win .. 9bi. 
Ideal foe above units. 
iS.19.fl. 



HhTONE RECORDING TAPE 



J 1001 Hiti L.P. 

j loo*.: 3tn t.p, 

J1003 Sin L.P. 

J1004 nil) D.P. 

JIOOS 6,In LP. 

JlOOti jj|lii D.F. 

JI007 Tin S.P. 

.11008 Tin L.P. 

J 1009 7ln D.F. 

J101D 7In T.P. . 

C$0 Caaset te (Liuiary cased) 

C90 Cassette (Library eased) 



BRITISH HADE TOP QUALITY 

225ft 5.6 Y. 4 P. 1,2 

BOOft 10/6 P. * P. 1/2 

900it 10/- P. & P. 1/8 

1.200ft 15/- P. * P. 1/8 

l.aooft is/a P. & P. 2/- 

1.800ft 2B/6 P. 4 P. 2/- 
l.aOOIt U/fi P. 4 P. 2/6 
1 ,800ft 17/8 P. & P. a/6 
2,40011 96/- P, & P. 2/8 
3,800ft 60/- P. & P. 3/6 
8 8 P. & P. 1/- 
16/- P. tP. 1/- 



PVC 

Poly 
PVC 

Poly 

pvc 

Poly 
PVC 
PVC 
Polv 

Poly 




C120 Cassette (Library eased | 18/- p! * P. 1/- 



COOl MULTI-TESTER NEW! 35¥88>§£ TJSSSfSgg? 




Over load prol ection 
'20,000 obius per volt; 
"i.e. v..!';- 10, SO, 
•260, 1,000V; d.e. 
volts 5-25, 125; 600, 
'2,600V; d.e. current 
0— 50f*A, G — 250mA: 
Resistance — 60k fl 
0-6MO ; decibels 
—20 to +22dB. Size 
ol meter 4) in ■ 3 J Si. :< lin. Complete with 
leather cue. 86/-, P. * P. 3/8. 



62 D.MULTI -TESTER 



20,000 ohms per volt; 

d.e. voltage 5, 2G, 60, 

260, 600V, 2-5kV (20,000 

ohms per volt), a.c. 

voltage 10, 50, 100, 500, 

1,000 V [10,000 ohms 

per volt); d.c. current 

O-50fiA, 0-2-5mA, 

0-250mA ; resistance 

0-6kO,ii-6MQ (300 obtiw and 30k f] M 

centre scale); capacitance 1QF to 001 til F, 

0. 00 1 nF to 01 -iFr decibels — 20 to +22rt B. 

Size 41 in ' 3Jin ■ Un. 71/-. P. * P. 3/8. 



LIND-AIR LA.20 





A lantiu-lk ettrto amplifier made exclu- 
sively for Lind-Air and represents con- 
siderable advance in solid state stereo 
amplifiers. Inputs for gram and radio 
tuner and provision for direct tape 
recording. Attractive and modern panel 
with bass, treble balance and volume 
controls also on /off and stereo/mono 
switch. Output SW per channel music 
power. Frequency response 40-20 ,000Hz 
8-16 ohm speaker matching, Size Ifijln 
- 14in : 4in. 

LIND-AIR 
PRICE 



22 Gns. 



SINCLAIR IC-10 
INTEGRATED CIRCUIT 

10W Amplifier. Size only tin X 0-4in 
0-2in. A true hi-ll amplifier complete with 
manual giving details of a wide range of 
applications and Instructions. Guaranteed 
I years. OKLY 60/6. P. & P. 1/6. 
SPECIAL TRAHSF0RMEK FOR OPERA- 
TDIS S1HCLATS IC-10 from a.c. mains 
230/250 V. Oolput 13V at 0-5A, 16,'fl. 



TELETOX STP. 800 8- TRACK STEREO CARTRIDGE HOME FLAYER 
A complete solid state mill ready to plug In and play. HI-FI reproduction 
at 3] i.p.s. Player unit Incorporate* volume, tone and balance controls 
and push-button track selector. Size 14|in x lOlln. Matched speakers. 

size 1 lin y 8lu a 5e in each. 




NEW from MULLARD 

U N I L E X Audio Modules 

Now you can build your own stereo units exactly as you want 

them, and entirely in your own home. 

A good quality stereo amplifier can be built with no electrical 

knowledge. 

All solid state — Baxendall tone control circuit — no soldering 

— terminal block connections throughout. 

Everything you need to know 
about UN1LEX SYSTEMS is 

in the Mullard book "Do it 
yourself stereo". Superb de- 
signs, detailed plans, simple 
instructions in non-technical 
language covering 4 systems in 
4 price ranges. 

Send for your copy now 5/- 
Post Free. 

UN I LEX Audio Modules 




Amplifier 
Module EP9000 



£2.18.0 each 



Pre Amplifier 

Module EP9001 £3,2.0 „ 

Power Supply 

Module EP90O2 £4.12.0 „ 

Control Panel| 

Assembly and 

Escutcheon 

Plate £3 . S.O „ 

BUILD A STEREO 
AMPLIFIER FOR ONLY 

£16.15.0 P. & P. 7/6 




DE-LUXE BTSBEO 
HEADPHONE! 

With soft . rubber 
earpieces. Imped- 
ance 8-16onms. Fre- 
quency response 23- 
13,00OHi. With 

lead and stereo plug. 

Onlj 68/6. P. * P. 

3'8. 



SOLDERING 
GUN 



Comfortable Grip 
with, trigger con- 
trol, "V" shaped 
31in. bit to 
minimise wear. 
Light beam is automati- 
cally directed on to end 
of bit when ON/OFF 
trigger is in use. 230-250 
volte. 86 watt element. 46. 6, P. & P. 3/6. 



S-DEC BREADBOARD 





Brilitk iiadt 
£olderle&& breadboard panels, for fast re* 
liable component connections. 
Single DeCs. One 8-DeC with Control 
Panel, Jig and Accessories for solder less 
connections to controls, etc., with booklet 
"Projects on 8-DeC" giving construction 
details tor a varietv of circuits. JSJvfl. 
P. A P. 2/8. 

4-DeC KIT, Four li-DeCs with two Control 
Panels, Jigs and Accessories and the book- 
let "Projects on S-DeC" all contained In a 
strong attractive plastic case, Ideal tor 
the professional user. 16,17.6. F. fc P. 
3/6. 
T-DeC KIT 16,17.8. F. A P. 3,8. 



HI-FI TURNTABLES 




2025 T/C with stereo cartridge . . IS.10.S 
3000 with Sonotone 9TAHCD 

stereo cartridge 110. IB, B 

SP26 Mk. II flO.lD.fi 

SL65B ilS.19.8 

Base and cover for above 16.10.6 

AP75 118,10.0 

SL72B 124.10,8 

SL75B «M,7,0 

SL95B £39.9 

401 128.10.0 

Base and cover for above 18,19.0 

P. & P. Decks, 12/6; Base and Cover, 10/-; 
Deck /Base/Cover, 17/6. 

SPECIAL 0FTEB81 

HF-2S Mk. II with base 114.10.0 

P. i P. 15/- 
SP25 Mk. II with SoiioKine 

STAHCD cartridge and base 116.16.0 

P. A P. 15/- 
Sonotone STAHCD cartridge . . , 12.16.0 
P. & P. LJL, 



18/19,25 & 53 TOTTENHAM CT. ROAD, LONDON W.1 
Telephone: 01-580 2255/4532/7679 

Open 9-6 pm. Monday to Saturday. Thursday until 7 pm. 



Ail Mail Orderi and correiBondence to Dept. 
Lt 10, Kitkmin House, 54*. Tottoalum Court 
Roil, Lonftn, W.l. Tel: 01-580 7041'!. 



Practical Electronics October 1970 



823 



Build a 

transistor radio 

in an evening 



stSW* 




- learn about radio and 
electronics at the same time 

There's no complicated soldering with the 
Radionic X30 Kit. The components plug in and 
your radio will work straight away. Build 33 
fascinating experiments : a printed circuittransistor 
radio, a burglar alarm, a morse code buzzer etc. 
Radionic kits are safe -they're battery operated. 
The X30 and more advanced Radionic Kits can 
help you with your exams too. Send off this 
coupon today. 

TO: RADIONIC PRODUCTS LTD.. PE ' | 

St. Lawrence House, Broad Street, Bristol BS1 2HF 

Please send me full details of all Radionic Kits/please send me one | 

Radionic X30 kit at 11 1 9s. 6d. {Delete where inapplicable. ) i 



Name. 



./''■?/ | 



Address. 




wn 



who wants a£2,000+p.a. 

opportunity in the dynamic 
new computer industry? 

In only 4 weeks you're in - and only 
the incredible Eduputer can make it 
possible. 

Now for the first time anybody can train outside the computer 
industry for a lucrative career as a computer operator, with 
actual experience on an Eduputer. 

Who created Eduputer? The internationally famous company 
Programming Science International, They developed it to the 
specific requirements of the massive New York city training 
board and its practical results have been one amazing success 
story, 

We are proud to have been selected as the only commercial 
training organisation permitted to use the Eduputer in the U.K. 
Thanks to Eduputer, nine out of every ten can learn to 
operate the most advanced computers in only four 
weeks. Unlike Computer Programming, no special 
educational qualifications and no maths required. Just 
you and the incredible Eduputer! 

Jobs galore! The moment you qualify, our exclusive computer 
appointments bureau introduces you to computer users every- 
where with good jobs to offer {up to £40 a week full-time, £50 
a week as a temporary). More than enough to go round, too — 
because 144,000 new operators will be needed over the next 
five years alone. 

This is your big opportunity to get out of a rut and into the 
world's fastest-growing industry. And remember — LCOT is the 
only commercial computer school to have Eduputer. it means a 
lot to employers. 

Telephone: (01) 437 9906 NOW! 

Or post the coupon today for full details FREE and without 
obligation. 



London Computer Operators Training Centre, 

B5, Oxford House, 9/1 5 Oxford Street, London W.1 . 

Telephone: (01) 437 9906. 

127/131 The Piazza, Dept. B5, Piccadilly Plaza, Manchester 1. 

Telephone: (061) 236 2935. 

Please send me your free illustrated brochure on exclusive 

Eduputer "hands on" training for computer operating. 

Name . 

Address 



824 



Practical Electronics October 1970 




A selection of readers' suggested circuits. It should be emphasised that 
these designs have not been proven by us. They will at any rate stimulate 
further thought, 

This is YOUR page and any idea published will be awarded payment accord- 
ing to its merit. 



Thereupon TR2 becomes forward-biased and con- 
ducts, causing almost the entire power supply voltage 
to be dropped across the solenoid X2. The collector 
of TRI is practically at earth potential, and the portion 
of voltage appearing across TR2 emitter and collector 
is potentially-divided by Rl and VR1, The resulting 
potential on TRI base is insufficient to allow TRI to 
conduct and so the solenoid X2 is energised, but the 
bell XI does not ring. 

If the bell-push is operated when any of Sl-3 contacts 
are not closed, or, S4 and S5 contacts are not open, no 
bias is fed to TR 1 base, and it will not conduct. Hence, 
the solenoid will not operate, and the entire battery 
supply voltage appears across TR2 emitter/collector. 
Part of this voltage is tapped off by the wiper of VR1, 
and the resulting voltage causes sufficient current to 
flow in TR2 to operate the bell XI. 

The bell-push can be operated by a caller, who does 
not possess a special "key" and the door-bell would ring 
in the normal manner. 



MAGNETIC COMBINATION LOCK 



The system described here has extremely high 
security characteristics, and its principles can be 
safely described in detail to the most doubtful looking 
individuals without fear of compromising the security 
of one's abode. The standard door-lock may be used, 
and the power normally associated with operating 
heavy lock plunger solenoids is thus unnecessary. 

The actual "key" comprises a coded array of tiny 
magnets, in which the physical positioning and mag- 
netic sense (i.e. position of N and S poles) form the 
secure code which alone will operate the simple circuit. 
Furthermore, attempts at solving the coded magnetic 
field will immediately result in the sounding of the 
doorbell, or, if desired, and outdoor alarm bell ! 

Use is made of the existing doorbell push so that if 
this is pushed in the normal way, the doorbell sounds. 
If, however, the special magnetic "key" is first correctly 
placed in position, and the doorbell pushed, the door 
lock is released. 

Circuit operation 

The circuit diagram Fig. 1 shows one configuration 
which applies for a certain combination, using five 
reed switches. The power supply to the entire circuit 
is broken by the bell-push S6. This ensures that no 
current is drawn from the battery except during the 
instant it is required. 

The reed switches S1-S5 are all miniature normally 
open contact types, i.e. their contacts remain separated 
in the absence of a strong magnetic field. S4 and S5 
have permanent magnets secured close to them so that 
they then perform as normally closed switches, which 
require not only an additional magnetic field to part 
their contacts, but such a field must be of opposite 
polarity to that of their fitted magnets, so that the two 
fields cancel. 

Unlocking 

For bias to be fed to TR2 base the following con- 
ditions must be obtained; SI, 2 and 3 contacts must be 
all closed; S4 and S5 contacts must both be open; 
and the door- bell push S6 must be operated to complete 
the voltage supply path. 




Fig. I. Circuit of the magnetic combination iock 

Components 

The solenoid X2 should be capable of operating at 
3 volts, and may be operated by a light-duty relay in 
TRI collector circuit, in which case a lower-power 
transistor may be used. Resistor values will depend to 
some extent on the types of transistors used, and VR1 
must be of sufficiently high resistance as not to conduct 
sufficient current from TRI collector to earth as 
to operate X2 (or relay if used) when TRI is not 
conducting. 

To determine the value of Rl connect up TR2 and 
X2 only, and connect a 50 kilohm potentiometer (set to 
maximum resistance!) between base and negative 
6V line. Vary the potentiometer, gradually decreasing 
the resistance until the solenoid or relay is operated. 
Disconnect and measure resistance arrived at; insert in 
circuit the next lower preferred value for Rl. VR1 
should be adjusted to make TR I ring the bell when the 
bell-push is operated without the magnetic key, but not 
to allow the bell to ring when TR2 is conducting. 

Solenoid 

The circuit described is intended to operate a 
manually-assisted arrangement, in which X2 merely 
removes a locking pawl from the standard door knob 



Practical Electronics October 1970 



825 



mechanism, so that the handle may be turned. How- 
ever, there are now available on the market electrically- 
operated solenoid locks, but care should be taken to 
choose a type which will operate from the power 
available, and which will not draw more current than 
can be safely supplied by the transistor or relay chosen. 



y 3 ^ 



Locator 

holt &pta— »Q 







S3 


( > 


S2 


t ) 


SI 


{ 1 


S4 

MAG 

S5 

NAG 


5=N 

1 > 




N S 



(A) KEY 

R«ar vie* 



(8) SENSING 
AREA 
Front view 



Fig. 1. Suggested arrangement of reed switches 

Key 

The form taken by the key is governed by the arrange- 
ment of the reed switches. Probably the most practical 
configuration for these is to arrange them in a single 
row, side by side, making sure that they are close enough 
to allow a key to be made of reasonable proportions, 
but not too close so that the field of the fixed magnets 
interact to give trouble, see Fig. 2. 

B. H. Baily, 
Dorset. 



NOVEL OSCILLATOR 



9V MOTOR 
PERMANENT MAGNET 
OC TYPE 
iQOjiF^. 2 OR 3 POLES 



BY1 
9V 




LSI 
MA 



R1 

z ■2nn; 




Fig. !. Simple oscillator circuit diagram 

Fig. 1 shows a simple and novel oscillator utilising a 
motor found in many model trains, cars, etc. When the 
spindle is rotated, the motor acts as a dynamo and the 
output is fed to the base of the transistor (any common 
type should suffice), which acts as a common emitter 
amplifier. 

The frequency of the resultant note depends on the 
speed of rotation of the motor. 

J. M. Maud, 

Scunthorpe, 

Lines. 



NEWS BRIEFS 



S.E1T. Computer Group 

To encourage Society involvement in the whole field of 
electronic data processing, the Society of Electronic and 
Radio Technicians has established a Computer Group 
Committee to organise Society activities in selected fields. 
Initially, the Computer Group Committee will be organis- 
ing meetings and procuring papers in the field of computa- 
tion. 

The committee will be made up of the following 
personnel: J. Harris (chairman), Kingston College of 
Further Education; D. J. Etennis, I.B.M.; K. R. Brown, 
B. Dobson and M. R. Fox, I.C.L. ; and J. Cairns, Univac. 

The first meeting to be organised by the Computer 
Group will be a lecture and demonstration by Mr C. J. 
Fleckney, Information Co-ordinator of I.C.L. to be held 
at the I.C.L. Training Centre, Icknield Way, Letchworth, 
Herts, on Wednesday, October 21, commencing at 
7.00 p.m. 

Navigation System Takes the Air 

A lightweight military navigation system announced by 
Marconi at the end of last year has started flight demon- 
strations to prospective customers in the Company's Piaggio 
aircraft. Aimed at a major slice of a prospective £4 
million European and U.K. market, this is the first time 
that this system has flown in Europe. 

The equipment, Type AD280, is designed to be mounted 
in the pilot's instrument panel, and to provide complete 
VOR and instrument landing facilities in a single unit, 
including all necessary controls. 

The navigation system is designed primarily for small 
high performance military aircraft, such as the Jaguar and 
the Phantom, and could also be applied to military heli- 
copters. 

Servicing will take the form of removing a faulty module 
and replacing it with a complete sealed unit. The faulty 
module will then be returned to the factory for repair or 
replacement. 

The system is the result of over a million dollars expendi- 
ture on research and development. Marconi intend to 
start production at their own factory in Basildon, Essex, 
and a new, thick-film assembly area will be laid down to 
produce the assembled substrates for this and other equip- 
ment which will be in production next year. 

Computers to Train Postcode Operators 

Postmen who operate postcode desk keyboards may in 
future be taught almost entirely by computer. In pioneer- 
ing this type of training, the Post Office is soon to take 
delivery of a computer which will individually control up 
to 20 trainees, allowing each to develop his or her skill at 
the most suitable pace. 

A keyboard simulation is flashed on a television-type 
screen before him; over this is a superimposed diagram 
showing how his fingers should be positioned. The letter 
to be typed will flash on the screen — the position of the 
flashing letter on the keyboard simulation corresponding 
with the position of the key which should be pressed. 

The aim is to produce operators capable of a speed of 
250 characters per minute with an error rate of only one in 
2,000 characters. The computer will be programmed to 
examine the pupil at every stage of training and give 
revision exercises or prolonged practice sessions on any 
weak point he may display. 

The first computer trainer will be installed at Croydon 
and the first full class of trainees should be under instruction 
by the end of the year. 



826 



Practical Electronics October 1970 



MICRO SWITCH 

5 amp. changeover contact*, 19 
each, IS/- doz. 1 & amp. modi;] 4/- 
each or 81/- doz. 



fc 



TOGGLE SWITCH 

3 amp. 250V with filing ring, 
each, 15/- dot. 



18 



CONSTRUCTORS' PARCEL 

1. Plessey miniature 2 gang tuning condemn 1 
with built-in trimmers anil wave gang switch. 
'2. Ferrlte slab aerial with coils to suit the above 
timing condenser. 3. Circuit diagram giving all 
component values for 8 translator circuit covering 
full medium wave and the long wave baud around 
radio 2, The three items tor only 7/8 which U> 
halt of the price ot the tuning condenser alone. 

SLOW MOTION DRIVES 

For coupling to timing comic use re, etc. One end 
Jin Hhalt, the other end Hts to a tin ahaft with 
grub screws. Price 4/6 each, 48- dozen. 

LARGE PANEL MOUNTING 
MOVING COIL METERS 

Size Sin :; 4in Centre zero .200-0-200 micro amp, 
made by Kangamo Weston. Regular price 
probably £S. Our price 5B/S. Ditto hut 100-0-liWI 
79/8. 

A.C. Ammeter 6 amps, iluah mounting- incying 
iron. Ex equipment hnt guaranteed perfect M'fl. 

CIRCUIT BOARDS 

Heavy copper on 3/82 paxoliu sheet ideal for 
malting power packs, etc., as aheet is very strong 
snd thick enough to allow copper to be cut away 
with hacksaw blade, C In 5in l'fl each 
Win ■ oln, «,'« each. 

8KVA Auto-trausfornier in ventilated sheet steel 
case- tapped. I10v-140v-170v-200v-230v. Ex 
equipment but guaranteed jierfecl £19.10.0. 
carriage at coal. 

PP3 BATTERY 
ELIMINATOR 

Kun your small traatcftor 
radio from the mains— full 
wave circuit. Made up ready 
to wire into your set and 
adjustable high or low current. 
B/8 each. 




- e== 



3- REED SWITCHES 



^ 



Ufaas encased, switches operated by external 
magnet — gold welded contacts. We can now offer 
8 types : 

MinUture. lln long :< approximately (in dia- 
meter. Will make and break up to [A up t<i ItOfi 
volts. Price B/8 each, 84/'- dozen. 
Standard, Sin long - A in diameter. This will 
break currents of up to 1A, voltages up to 2011 
volts. Price 8/- each, 18/- per dozen, 
Kit. Flat type, 2 in long, just over A In thick, 
flattened out, so that it can be fitted into a 
smaller space or a larger iiuantity may be packet] 
into ft square solenoid. Rating 1 amp 200 volts. 
Price 8/- each. 83 per dozen, 
8mall ceramic magnets to operate these reed 
switches 1/8 each, IS/- dozen. 

OOOSmFd TUNING 
CONDENSER 

Proved design, Ideal for straight or 
reflex circuits 8/8 each, M/- dozen. 

SUB-MINIATURE MOVING COIL 
MICROPHONE 

a* used in behind the e»r deaf-aid* 

Acts also as earphone size only [in X I In :; (in. 
Regular price probably £3 or more. Our price 19/8. 
Note these are ex equipment but it not in perfect 
working order they will be exchange*!. 

CHART RECORDER MOTOR 

Small (21n diameter appro*,) instrument motor 
with fixing flange and spindle (Jin long, tin 
diameter) Integral gear box gives 1 rev, per 24 
hours, IP, 6, 

IGNITION (E.H.T.)TRANS FORMER 
Made by Farmeko Ltd., Primary 240 V SOHz. 
Secondary 6kV at 23mA, Size appro*. 4|in 
3 r in 2Mn thick. 88/8 pliw 4.'fi P. A P. 

II VOLT 

EXTRACTOR FAN 
BY DELCO 

Ideal for ventilation in Caravan, Car or Boat. 
•S Bladed oin diameter fan Inside heavy duty 
cylinder with 3 point fixing flange. fijln diameter 
fixing hole. Length approx. 8 J In. Except ional 
bargain 87/6 plus 6/6 post and insurance. 

NEED A SPECIAL SWITCH ? 
Double Leaf Contact 

Very alight pressure 
f= closes both contacts, 13 
each, 12/-,doz, Plastic 
push -rod suitable for 
operating, 1/- each, 9.'- 
dec. 

COMPUTER MULTI-CORE 
CABLES 

12, 14/0076 copper cores, each one Insulated by 
eoloured P.V.C. then separately screened, the 12 
metal braided cores laid together and P.V.C. 
covered overall making a cable lust under ) in. 
dia. but quite pliable. Price 7/8 per ft. Any 
length cut. Other sizes available 7 core 8- ft,. 
8 core </- ft., 4 core 3/fl ft. 



RE-CHARGEABLE TORCH 

>ieat flat torch, fits unobtrusively in ynut pocket, contain* 
2 Nicad cells and built-in charger. Plugs into shaver adaptor 
and charges from our standard 200/240 volt mains. American 
made, sold originally at over 4 cioll'lru. Our price only 
19/8 each. 




INTEGRATED CIRCUIT BARGAIN 

A purcel ol integrated circuits made by the famous Plessey Company. A 
once- in-. [-lifetime offer of Micro-electronic devices well below eoBt ol manu- 
facture. The parcel contains a ICs all new anil perfect, first-grade device, 
definitely not sub-standard or seconds. The ICs arc all single silicon chip 
General Purpose Amplifiers. Regular price of which la well over <1 each. Full 
circuit details of the ICs are Included anil In addition you will receive a list 
of 50 different ICa available at. bargain prices 67- upwards with circuits and 
technical data of each. Complete parcel only Ml post paid; or List and all 
data 10'- post tree. Credited when you order ICs value 30/. and upwards. 



15. 30, 40 4 100 WATT HI-FI SPEAKERS 
FULL Fl 18 HTCH LOUDSPEAKER, This is undoubtedly 
one of the finest loudspeakers that we have ever offered, 
produced by one ol the country's most famous makers. It 
has a die-cast metal frame and Is strongly recommended 
for Hi-Fi lead and Rhythm Guitar and public address. 
Flux Uensity 11,000 gauss-Total Flux 44,000 Maxwells- 
Power Handling 10 watts it. M.S. Cone Moulded flbre- 
Freq. response 30-10.000 e.p.s.— Specify 3, or 15 ohms — 
Mains resonance tiO e.p.s.— Chassis Dlam. 12in.— 12(in. 
over mounting lugi— Baffle hole llin. Dlam.— Mounting 
holes 4, holes— Jin, dlam, on pitch circle lljin, dlam.— 
Overall height 5) In. A £0 speaker offered tor only £3.19.6 
plus 7, 8 p. ftp. 12iu. 40 watt 88.19,8 plus 8/6 p. ft p. loin 
25 watt 87.19.8 plus 10/6 p. ft p. ISin. 100 watt 119.18.0 
plus 80/- p. it p. 




THIS MONTH'S SNIP' 

25 Amp Electrical Programmer 

Learn in your sleep: Have Radio playing and 

kettle boiling as you awake- — switch-on. Lights to 

ward "ff intruders- have warm house to come 

home to. All these and many other things you can 

do if you invest in an Electrical Programmer. 

Made by the famous Smiths Instrument Company. 

Thisia essentially a 230/240 volt mains operated Clock and a 20 amp Switch, 

the switch-off time of which can he delayed up to 12 hours (continuously 

variable not stepped). Similarly the switch-on time can be delayed. This is 

;i U-aiitiful unit, size 5J X :<} < 2} in. deep. Metal encased, glass fronted 

with chrome surround. Offered at 47'8 plus 3;fi postage and Insurance. 




MOTORISED SWITCH 
For Animated Sign*, etc. 
This is a motorlsed programmer switch, mains 
operated, with six 15 amp changeover contacts 
operated by triggers on a rotating drum. Six 
triggers will put switches down. Also simple on/off 
operation or chaiigeovers arc passible. The* 
triggers are exactly set to any position around thd 
drum which is rotated by a one rev. per hour 
motor, (Motors with other apceds available.) A 
beaut iiully made precision switch which probably 
cost in excess of £20. Limited quantity only £11.15 
each, post free. 




neon warning light in metal box 

complete with 7 feet of heavy cable 

39/8 wired up, ready to work plus 4/6 post ami insurance 

6 amp 3 pin mod;! 38,'-. 1 5 amp 3 pin model 4S/-. 



DISTRIBUTION PANELS 

Just what you need for work bench or lab. 
4 :-: 13 amp sockets and on/off switch with 
Takes standard 13 amp fused plugs. Supplied 



^^—^—— BARGAIN OF THE YEAR 
MICROSONIC KEYCHAIN RADIO 

7 transistor Key chain Badlo In very pretty 

case, size 2 1 x 2 5 •■: liin— complete with 

soft leather zipped bag. Specification: 

Circuit: 7 translator superheterodyne. 

Frequency range: 530 to 1,600 Kc/s. 

Sensitivity: 5 nrv/m. Intermediate 

frequency: 485Kc/s or 455Kejs. Power 

output: 40riAV. Antenna: lorriterod. 

Loudspeaker: Permanent magnet type. 

Ill transit from the East these sets suffered 

slight corrosion as the batteries were left in them hut when this corrosion 

is cleared away they should work perfectly— offered without guarantee 

except that they are new. Price only 84/8 plus 2/6 poet and insurance, less 

batteries, for £7, post iitc. 




MAINS TRANSFORMERS 

Note all these are first grade Transformers uat 
all have normal 200/240 volt 50 cycle prlmarv. 
Mains Transformer Type Ho. 88788 
Upright mounting, size 3 x 2J x 21n. approxi- 
mately. 1 secondaries one 28 volt 1 amp and the 
other 5 5 volt IS amp. Earth screen between 
primary and secondaries — this transformer will 
power a 5-5 watt stereo amplifier (circuit diagram 
available, price 8/8), Sultahle output transformer 
is type 66787 described hclow-. Our price 17/8 
plus 4/6 post. 

Maim Triniformer Type Mo. 88788 
i 'hassle mounting type, size approximately 3 - 2| 

< 31m. 2 secondaries one 280 volt at 60 mA and 
other H-3 volts IE amp. Earth screen between 
prlmarv and secondaries. This will power a 5 watt 
.unplifler (circuit available 2/8). Matching OPT. is 
56734 described below. Price 18/8 plus 4/6 poet. 
Maini Transformer Type No. 86898 

Fprlght mounting, else approximately 4x8 

< 2 J In. 2 secondaries 275-0-275 at 90 mA and 
6-4 volts at 31 mA. There Is a screen between 
primary and secondaries. This is a partner to out- 
put transformer 50694 described below. Price 
19/6 plus 4/6 post. 

HEAVY DUTY MAINS 
TRANSFORMER 
30V. 37A. Primary tapped 200/240 III lOv. steps. 
K really beautiful "C 4 * core transformer. Made by 
I'arnicko, impregnated and varnished, Weight 
approx, 50 lb,, size approx. Sin. wide Hjin. deep 
and 6|ln. high. Metal framed for tree standing and 
fitted with E.S. screen. Probably priced £40-£50 
from Farmeko, Ex equipment, hut perfect, £17.10 
each, plus carriage at cost. 

OUTPUT TRANSFORMERS 

OPT. re!. 88894 

Chassis mounting — size 2 -.: 2 X 2in. approxi- 
mately 7 watts. A push pull transformer for 
matching 2/EL84 or similar valves to 15 ohm 
loudspeaker. 14/6 no extra for post If ordered 
with Transformer 56690, Circuit diagram of 
amplifier available, price S/f. 
OPT. Ml. 88787 
I'pright mounting, size approximately 21 ,< 2 

I 2in. Matching impedance 80 ohms to 18 ohms. 
D watts output using transistor type AD140 
(Circuit diagram available price S/8), Price 8/8 
each, no extra tor postage If ordered with mains 
transformer type 06788. 
OFT. rel, 888004 
Ifprlght mounting, size approximately 2 x 2} 

, 2in. Primary impedance 60 ohm, secondary 
impedance 3 ohm. otherwise this is as 66787. 
Price 8/S. 
OPT. wf. 58784 

Chassis mounting, size approximately 2± :< 2 
Ijiu. Primary 500 ohm centre tapped, Batio 
27/1. 5 wattn output using twin ELL80 or similar 
Price 18/8. No extra for postage if ordered with 
.86733. 

50 CYCLE TO M CYCLE INVERTERS 

For operating American instruments and other 
equipment made for 60 cycles ] 15 v. from 230/240 
60 cycle ma: oh. These units have an output of 
110 volts A.C. and will handle a load of up to 
100 watts. These are precision made and have a 
reed typo frequency meter which vibrates when 
the frequency Is exactly SO e.p.s. Adjustment of 
the frequency is by a knob on control panel. Input 
by 3 core output from 3 pin socket. Original cost 
of this in excess of *60. A 1 1ml ted quant ilv available 
817.10, each. 

MINIATURE 
WAFER SWITCHES 

2 pole, 2 way — 4 pole, 2 way- 

3 pole, 3 way— 4 pole, 3 way— 2 
pole, i way — 3 pole, 4 way — 2 pole 
6 way— 1 pole, 12 way. All at 8/8 
each. 38/- dozen, your assortment 



WATEPRBO OF HB ATUtO 

ELEMEKT 
26 yards length 70W. Self- regulating 
temperature control. 10/- post free. 



THE 5-5 WATT STEREO AMPLIFIER 

Made by one of our most famous makers for a de-luxe player. This amplifier has 
a quality of reproduction much lietter than average. Using a total IS transistors 
and a generously sized mains power pack. Control* include bass, treble, balance 
and volume. Suitable for 8- 16 obms impedance speakers with crossovers for 
tweeter mid -range and basa thus giving option of 1, 2 or 3 speakers per channel. 
Offered at about one third of Its original price only £9.19.6 plnw ttffl post rind 
insurance. 





3 IcW TANGENTIAL HEATER UNIT 

This heater unit is the very latest type, uiott 
efficient find quiet running. Is ue ntted In 
Hoover and blower heaters coating £16 and 
more. We have a tew only. Comprises 
motor, impeller, 2k1>V element and lkW 
element allowing switching 1, 2 and 3k W 
load with thermal safety cut-out. Can be 
: fitted into any metal line case or cabinet. 
Oidy need control Bwitch. 79/8. 2k\V 
Model :ia above except 2 kilowatts 89/6. 
Postage and insurance 6/6. Don't miss this. 



MAINS OPERATED CONTACTOR 

220,240v, 60 cycle solenoid with 

laminated cote so very silent in 

operation. Closes 4 circuits each 

rated at 10 amps. Extremely 

well made by a German Elec- 
trical Company, Overall size 

2{ { 2 x 21n. 18,8 each. 

AUTO-ELECTRIC CAR AERIAL 

with dashboard control switch- 
fully extendable to 40 in. or fully 

retractable. Suitable for I2v 

positive or negative earth. Supplied 

complete with fitting instructions 

and ready wired dashboard switch. 

£8,18.6 plus 0'- post and ins. 

MAINS MOTOR 
Precision made — as 
used in record decks 
and tape recorders- 
ideal also for extractor 
fan, blower, heaters, 
etc. Sew and perfect. 
Snip at 9/8. Postage 
for drat one then 
1 /- for each one 
ordered. 12 and 
over post free. 



Where postage ia not stated then orders 

over £5 are post free. Below £5 add 2 '9. 

9.A.E. with enquiries please. 




ELECTRONICS (CROYDON) LTD 

Dept. PE, 266 London Road, Croydon CRO 2TH 

Also 101/1 Tamworth Road, Croydon 



Practical Electronics October 1970 



827 



W&l A FAST EASY WAY 
TO LEARN BASIC RADIO 
AND ELECTRONICS 



* 



Build as you learn with the exciting new 

TECHNATRON Outfit! No mathematics. 

No soldering — but you learn the pmtical way, 



Now you can learn basic Radio and Electronics at home — the 
fast, modern way. You can give yourself the essential technical 
'know-how' sooner than you would have thought possible — 
read circuits, assemble standard components, experiment, 
build . . . and enjoy every moment of it. B.I.E.Ts Simplified 
Study Method and the remarkable new TECHNATRON Self- 
Build Outfit take the mystery out of the subject — rjiake learn- 
ing easy and interesting. 

Even if you don't know the first thing about Radio now, 
you'll build your own Radio set within a month or so! 

and what's more, 
YOU'LL UNDERSTAND 
EXACTLY WHAT YOU 
ARE DOING. The Tech- 
natron Outfit contains every- 
thing you need, from tools to 
transistors . . . even a versatile 



Multimeter which we teach 
you how to use. You need 
only a little of your spare 
time, the cost is surprisingly 
low and the fee may be paid 
by convenient monthly instal- 
ments. You can use the 
equipment again and again — 
and it remains your own 
property. 

You LEARN-but it's as 

fascinating as a hobby. 

Among many other interest- 
ing experiments, the Radio 
set you build — and it's a good 
one — is really a bonus; this is 
first and last a teaching 
Course, But the training is as 
rewarding and interesting as 
any hobby. It could be the 
springboard for a career in 
Radio and Electronics or 
provide a great new, spare- 
time interest. 



BRITISH INSTITUTE OF 
ENGINEERING TECHNOLOGY 

Dept. 371 B, Aldermaston Court, 

Aldermaston, Berkshire. 



A 14-year-old could under- 
stand and benefit from this 
Course- — but it teaches the 
real thing. Bite-size lessons— 
wonderfully clear and easy to 
understand, practical projects 
from a burglar-alarm to a 
sophisticated Radio set , . . 
here's your chance to master 
basic Radio and Electronics, 
even if you think you're a 
'non-technical' type. And, if 
you want to carry on to more 
advanced work, B.I.E.T. has 
a fine range of Courses up to 
A.M.I.E.R.E. and City and 
Guilds standards. 

Send now for free 1 64-page book. 

Like to know more about this 
intriguing new way to learn 
Radio and Electronics? Fill 
in the coupon and post it 
today. We'll send you full 
details and a 164-page book 
—'ENGINEERING OP- 
PORTUNITIES'- Free and 
without any obligation. 




ALDERMASTON COURT, 



POST 
CO(/POA/ 1 



To: B.t.EX, Dept. 3716, 
ALDERMASTON, BERKS. 

I would like to know more about your 
Practical Radio & Electronics Course. Please 
send me full details and-FREE 164-page book. 

name 



address 



MOWfh age. 



BI-PAK=L0W COST I.G's 



Bl-FAK Semiconductors now offer you the largest and most 
popular range of I.C's available at these EXCLUSIVE LOW 
PRICES. TTL Digital 74N Series fully coded, brand new. Dual 
In-line plastic 14 and 16 pin packages. 




ai-PAK 

Order Ho. 
BPOO 74D0N 
BPD1 740 IN 

BP04 74G4N 
BP10 7410N 
BP20 7420N 
BP30 743014 
BP40 7440N 
BF41 7441N 



BPS3 7463N 

BP80 7460N 
BPTO 7470N 
BF72 7472N 
BF73 7473N 
BP74 7474N 
BP7U 747BN 
BP76 7476N 

BP83 7483N 
BP90 7490N 
BF82 7492N 
BP93 7493N 
BF94 7494N 
BP9B 7495K 
BP96 7498N 



Simular Tnti to :- Description 

Quad 2-Inpnt NAN D GATE 

Quad 2-Input NAND Gate— OPEN 

COLLECTOR 

HEX INVERTER 

Triple 3-Input NAND GATE 
Doal 4-Input NAND GATE 
Single 8-Input NAND GATE 
Dual 4-Input BUFFER GATE 
BCD to decimal decoder and MT 

Driver 
BCD to decimal decode (TTL O/FJ. . 
Dual 2-Input AND/OR,'NOT GATE 

— expandable 
Single 8-Input AND/OR/NOT 

GATE — expandable 
Dual 4-Input — expandable 
Single JK Flfp-Flop— edge triggered 
Single Master Slave JK Flip-flop . . 
Dual Vaster Slave JK Flip-flop . . 
Dual D Flip-flop 
Quad Bistable Latch 
Dual Master Slave Flip-Sop with 

preset and clear 
Four Bit Binary Adder 
BCD Decade Counter 
Divide by 12 4 Bit binary counter. . 
Divide; by 16 4 Bit binary counter. . 
Dual Entry 4 Bit Shift Register 

4 Bit Up-Down Shift Register 

5 Bit shift register 



Files and at*, prices 
1-94 20-99 100 up 

are tit m 



Data la available for the above Series of Integrated circuits l! 



0/B 


SB 


4/0 


e/o 


6/6 


4/6 


tie 


6/8 


4/0 


m 


6 6 


4/0 


ere 


SB 


4/e 


6/8 


e/e 


4/0 


MM 


Mh 


17/8 


DU/6 


MI- 


17/8 


e/e 


HB 


4/0 


ere 


B79 


4/0 


e/e 


5 6 


4/e 


91- 


th 


7/- 


B- 


8/- 


71- 


10/- 


8/- 


m 


10/- 


sv- 


8/a 


n/- 


10/- 


o/e 


ii/- 


10/- 


e/e 


»« 


£28 


20/- 


ffl/6 


80/- 


17 a 


KM 


80 


17/0 


BtM 


20/- 


17/0 


we 


20/ 


17/0 


Kits 


80/- 


17/0 


M/- 


21/- _ 


IB 8 


n booklet lorm, price 8/6. 


Pries each 




1-24 


26-98 


100 up 



BBAHDNEW. FTJLL TO MAJITJFACTTJRERS' 

BPECD7ICATI0B 

BP709 Operational Amplifier, dual-In-line 14 pin pack- 
age = 3N72709 and similar to MJC709 and ZLD709C. . 10/6 0/- 8/- 

Thls Is a high performance operational amplifier with high Impedance differential 

InputB and low Impedance output. 



TTL INTEGRATED CIRCUITS 

Manufacturers' "Fallouts"- out of spec, devices Including functional """<> md I'M 1 
functional but classed as out of spec, from the manufacturers very rigid specifications. 
Ideal for learning about I.C's and experimental work, on testing, some will be found 
perfect. 



PAS Mo. 






uieoo = 


8 x 7400N . . . 


10/- 


uieoi -. 


6 x 7401N 


... 10/- 


U1C02 - 


6 x 7402N . . . 


... 10/- 


D1C03 = 


6 x 7403N . . . 


... 10/- 


D1C04 = 


6 x 7404N . . . 


10. 


TTIO06 = 


6 x 740SN . , , 


. 10/- 


UIC10 = 


6 x 7410N . , . 


.,. 10/- 


UIC20 - 


S x 7420N . . 


... 10/- 


UIC40 - 


S t 7440N . . . 


... 10/- 


mc4i = 


8 x 7441AN 


10 


UIC42 = 


6 x 7442N . , . 


... 10/- 


uieeo = 


G x 7480N . . . 


. .. 10/- 


uicei = 


6 x 7451N . . . 


. .. 10/- 


TJIC80 = 


5 X 7460N . . . 


... 10/- 


T/IC70 = 


S x 7470N . . . 


... 10/- 


TJTC72 = 


6 x 7472N . . . 


... 10/- 



PAS 31b, 






UI073 
UIC74 


Z 


8 x 7473N .... 
5 X 7474N 


10/- 
. 10/- 


UIC78 

UIC76 
UIC8Q 


- 


S x 7476N .... 
B x 7476N .... 
S x 7480N .... 


. 10/- 
. 10/- 
. 10/- 


UIC82 
L'ICS3 


= 


8 x 7482N .... 
6 x 7483N .... 


. 10/- 
10/- 


UIC88 
UIC90 


= 


5 x 7486N 

5 x 7490N 


. 10/- 
. 10/- 


UICB2 
UIC93 
UIC94 


= _ 


S x 7492N .... 
i x 74B3N .... 
8 x 7494N .... 


10/- 
. 10/- 
. 10/- 


T71C9B 

uicoa 

CTCX1 


2 


8 x 7495N .... 
8 x 7406N .... 
20 x ABST'D 74'l 


. 10/- 
. 10/- 

. so/- 



Packs cannot be split but 20 assorted pieces (our mix) is available as PAK UICXl- 
Every PAK carries our BI-PAK Satisfaction or money back GUARANTEE. 



DUAL-IN-LIKE LOW PROFILE SOCKETS 

14 and 16 lead sockets for use with DuaHn-Llne Integrated Circuits. 

Price each 
Order No. 1-24 26-99 100 up 

TS014 14 pin type 7/6 0/- 5/8 

TS016 16 pin type 10/- 8/6 7/0 



RTL FAIRCHILD (U.S.A.) I.C's 

BTL Micrologic Circuit* Qt*. &<** *»<* _ 

Epoiy case To-S temp, range 15=C to 66°C . . 1-11 12-24 28-99 160 + 

)uL 900 Bafler 8/- 7/- 8/6 6/6 

lib 914 Dual two-Input GATE 8/- 7/- 6/6 6/6 

^L 923 J-K Flip-flop 10/8 10/- 8/0 0/- 

Full data and circuits for IC'a in Booklet form price 1/6 each. 

(1A703E Linear RF-1P AMPLIFTER . . . . 11/- . . 10/- »/- 8/8 

FLA8TIC CASE To-S 6 lead up to 100 m/cs. 



DTL DIGITAL I.C's 

DTL dual in-line package. Price 

Typt MC844P expandable dual 4-input NAND Fower Gate 10/- each 

Type MC848P Clocked Flip-flop 18/- each 

Type 862 Triple 3 Input NAND/NOR Gate 10/- each 

FTJLL DATA SUPPLIED WITH UNITS 



Please send all orders direct to our warehouse and despatch department. 

BI-PAK SEMICONDUCTORS 

P.O. BOX 6, WARE, HERTS. 



Postage and packing add 1/-. 
10/-. Cash with order please. 



Overseas add extra for Airmail. Minimum order 



828 



Practical Electronics October 1970 



VALUE ALL THE WAY 



LINEAR 

INTEGRATED 

CIRCUITS 

RI-PAK MONOLITHIC 
AMPLIFIERS 
TO-5 3 1r«c 

BP709C, Operational amp- 
lifier. 16/- each, 

BP70K', OtJerjitliiiiitl amp- 
lifier (with '/.: uei mit- 
putl. 18 8 each. 

BP702*'. Operational amp- 
lifier (with direct ..ut- 
put), 12/ 6 each. 

BP50I. Wide bond . mi]. Ji- 
tter. 18/- each. 

BP52I, Logarithmic wide 
haii. i imp., 14/- each. 

BP20/C, General purpose 
amplifier (TO-0 S lead), 
(voltage or current amp.}, 
12/9 each. 

LC, Operational Amplifier 

with Zcncr output. 

Type 70IC. Ileal for P.E. 

Project*. H Lead TO-5 case. 

Full .tain.. 

Our price 1 2/ 6 each 
8 oil 11. each. Large Qty. 
Priee* .(note.-, hr* 



IC AMPLIFIER 



Identical encapsulation and 
pin con II cur at ion to the 
following: SL402-3. 1010 
and IC403. Each circuit 
incorporates a pre-um|! and 
class A.B. Power amp stage 
capal>l.- oi delivering up to 
3 watts RMS. Fully tested 
and guaranteed. Supplied 
complete with cire nit details 
and data. CODED BP.10I0. 
OUR LOWEST PRICE 
30.- each. 1 up 25 - each. 



MULLARD I.C. 

AMPLIFIERS 

TAA243. Operational amp- 

liitcr, 70,'- each. 
TAA203, Linear AK itmpli- 

tk'r, 15'6 each. 
TAA2P3, General purpose 
amplifier, 21/- each. 



CA3020 RCA (U.S.A.) 

LINEAR INTEGRATED 

CIRCUITS 



OTHER MONOLITHIC 

DEVICES 

D13D1 Silicon Collateral 

switch 10/- each, 
A SUCOU Planar , mouo- 
litlile integrated circuit 
having thyristor electrical 
characteristics, hut with an 
MMdC irate 5nd a built-in 
"Zener" .Mode l>elween 
gate and cathoik'. Full 
data uij.1 application cir- 
cuits available on request. 



Silicon Microwave Diodes — 

St Irani a (U.S.A.) 
1X218 and 1N218R 
matched pair a. Band 
mixer. Max. overall noise 
faction 13'7tlB at 3.000rn/es 
Brand new and boxed. 
Clearance Price 8/- pair. 



EX-E8UIPMBNT 
MULLARD 
API 17 transistors. Large 
can 4 lead type. Leads 
cut short bnt still usable, 
real value at la lor 10/-. 



AD 161 

AD 162 



t'.vr 



MATCHED roMPLE- 
M BNTARY PAIRS 

OP GERM. POWER 
Tit AGISTORS. 
For mains driven out- 
put stages id Amplifier* 
sliiiI Radio receivers. 



high power sili- 
con PLANAR TRAN- 
SISTORS. T0-3. 
FERRAXTI ZT14S7 

N P.N 



Vilpai 



VCB4U 
VEBN 



II I \ 

rr. lM/iai 

Plot . 75W 
lir'K 10-45 



PUKE 15/- EACH 



POWER KPN 
OlIiPKTCEie/OKACH 



OF 



FULL RANGE 
ZENER DIODES 

VOLTAGE RANGE 

S-18V. 400mV (DO-7 
Case) 8/6 ea. I J\V (Top- 
Hat) 3/6 ea. 10W(SO-10 
Stud) %h ea. All fully 
tested a ,, toi, and 
marked, statu voltage 
r,:.i:lin;,;. 



BRAND NEW TEXAS 
GERM. TRANSISTORS 
Coded end Guaranteed 
Pak No. EQVT 

Tl B 2U371A OC71 
T2 8 2G374 OC75 
T3 fi 'JG3744A OC81D 
T4 8 2G381A OCS1 
T5 8 2G382T OCS-2 
To 8 2G344.Y OC44 
T7 8 2G345A OC45 
TH M 2G37N OC7S 
Til M 2G399A '2X130^ 
TI0 8 2G417 AF117 
All 10. each pack 



2N2080 HFN SIX. DDA1 
TRANS. (■ODE D1G93 
TEXAS. Our price S/- 
eaeh. 



120 VCB NIXIE DRIVER 
TRANSISTOR. Sim. 

HSXMl ,v C407. 2X1893 
FULLY TESTED AND 
CODED ND130. I-'J4 3'B 
each. To-5X,l\N\ 23 up 
3. - each. 



Mil. Iran*, unliable for 
P.E. Organ. Mctnl TO-1 8 
Bqvt. 2TXSO0 l/-each. 
A.,y Qty. 



FREE 

One 10 - Pack ol your 
own choice Iree with 
orders valued £4 or over. 



KING OF THE PAKS Unequalled Value and Quality 



SUPER PAKS 



NEW BI-PAK UNTESTED 
SEMICONDUCTORS 



BatfetfacU n AUAKTEEIi in Kvcrj Pak. or n.one.v back. 

Pak Xo. 

UI 120 Glass Sab-iuin. t . t ner'd Put |w sc Oenual ii uni Diode s . 10. - 

L"2 _ 80 Mlxeil G ermanium Transistors AF/RP ■ ',. 10/ - 

l:t 75 Ueriiiiinl mn Gold Bonded Diodes elm. OAfl, OA47 . . . . . ,. Uh 

I '4 40 Germanium Truf-Histors like < )t '-s 1 . AC 138 10/- 



60 200mA Suti-ii.lii. : 



30 Silicon Planar Transistors SI'S aim. DSY95A, 2X7(W 



I.7 

Oh 
65 
in 
rjia 

U14 

uis 

£17 
UI8 

trnr 

U20 

121 

[-.•as 

V24~ 
C25 

U2b~ 

i as 



IB Wll lcmi Keet illefH Tr jp-Hai 75l)iu A up t o 1,000V 10 , 

■finar Iiiridcis 250mA OA/200/2C12 '. . 10r 

20 Mlxeil Volts 1 w alt Zene r Dio"des^ ._. .... 7T7T .'. ~ 10, ; 

_3» PS P ^uTcon Pl anar Tranjlnturii TO -5 aim . 2NU32 . . '. '... 10/ 

30 P NP->'P>' Mil. Transisto rs OC 200 & 2M lot ._.'. 10 

150 Mixed Silicon an. I licrmaulunt Diodes . , It/' 

25 N PS .SilicoVVlaiinr TraiiitistiuVTO-a sliu, 2S69Y. . 7. . . . , 10^ 



10 3-Auip Slllcoti Rectifiers stud Type up to 1000 P1V 10' 

w 

lo 



30 (icniianjoiii PSP A¥ Translators TO-5 like ACT 17 



d 8- Amp Silicon Rectifiers ByZ13 Type up to 800 PI\" 



25 Sillmti NPS TraiislstorH liko BC16S 10/ 



J 2 J'0-anip Sillcou llectltlerg Tu|i>Ual up lu 1 .000 P1V 10'- 

30 A. P. Ciermanimn alloy Transistors 2G3O0 Series A OC71 . . 10.'- 

10- 
"Mi 

10 

To - 



30 Maiit'a like MAT Series EOT Transistors 

20 (lerinaiiium 1-amp Rectltlers GJMup to 300 PIV 



25 300Mc.s XPS silicon Transistors 2X708, BSY27 



30 Fast Switching Silicon Diode* like 1X014 Micro-niln 



Exijerimcntcrs' Assortment of Integrated Circuits, untested. 

Gates, Fllp-Fklps, Registers, etc., 8 Assorted Pieces 20/ - 

U29 10 1 amp KCR's T0-5 ciu up to 600 PIV CRS I 25-800 20- 

t"3l 20 Sll. Planar NPN trans, tow noise Aiup 2X3707 M/- 

U32 25 Zener diodes 400m\V D07 ease mixed Voits, 3-18. 10,'- 



1.'33 
U34 
U35 

iJaa 



15 Plastic ease 1 amp Silicon rectifiers 1S40W series 10/- 

.... 7~i0 7 - 
W- 

Io/^ 

uf- 



30 Sll. PXP alloy trans. TO-5 8CY26, 2S302 4 

25 Sil. Planar trans. PXP TO-18 2N2900 

25Si"l. Planar XPSJ trans. TO-6 BFYoO/51'52 . 



U37 30 Sil. alloy trans. SO-2 PXP, OC200 2S322. 

U8H 20 Fast Switching BtL trans. SPX, 400Me/s 2X3011 10^ 

raw 30 RF Germ. PKp trans. 2N1303/0 TO-fl ~. 10/- 

U40 10 Dual trans. 8 lead TO-S 2X2060 10/- 

U41 
1.42 



•J5 KV tJenii. tram. TO-1 OC45 XKT72. . 



10 VHK (Jenn. PSP trans. TO 1 XKT0<57 AfllT 



.... 10/- 

Ui 

Co.le S'os. tiicutioiied above are given as a guide lo the type o( device in 
the Pak. The .leviees themselves are normally mimarked 



N PS I) I PFDSED 

SILICON PKOTO- 

DUO-DIODK TYPE 
IS701 (2X317S) for Tape 
Readout, high switching 
and measurement indi- 
cators. 50V, 200mW. 
OCR PRICE 10/- EACH, 
60 OR OVF.R 8,0 EACH, 
FULL DETAILS. 



NEW LOW PRICE TESTED S.C.R.'s 

1A 3.V 7A 18.4 JlOA 



400 
r',00 
-ini 1. 



FET'S 

2x saiy 

2X 3820 
MPFlOu 



lo- 
ss- ■ 
8,'- 



LOW COST F.E.T.I 
Fully Tested , ( ; uaranteed 
l'erameters t-quit. to 
2X3810. MPF102, 2X- 
615t>. 1-24 7/8 each; 
25-M1 8/3 each; 100 up 
S/8 each. Cede.! FE1B. 
Full data sent. TO-72 
case. 

CADMIUM CELLS 

ORP12 8/6 
OKPuO. ORP'il 8. -each 



PHOTO TRANS. 

OCP71 Type- 8 6 



[TO-fi (TO-WI [T0.4C 


(TO-4H 




case) 


case) 


case) 


ease) 




each 


each 


each 


each PIV 


each 


4 8 


ti- 


8/8 


10/6 23 


20.- 


S/- 


nt 


10/6 


12/6 50 


88/- 


71- 


7(6 


11/8 


IS. 1 - 100 


28'- 


8/6 


8/6 


13/6 


18/6 200 


32/- 


10/6 


11/6 


15/6 


26/- 400 


8S- 


12 6 


14 


18- 


30/- 800 


80- 



2 A POTTED BRIDGE RECTIFIERS. 
98*V 10/-. 



TRANSISTOR EQUIVALENTS BOOK. A 

complete cross reference and equivalent 
book for European, American and Japanese 
Transistors, Exclusive to Rl-PAK. 18/- each. 



PRINTED CIRCUITS 
EX-COMPUTER 

Packed with semiconductors and cum- 
IMmento, 10 boards give a guaranteed 
30 trans and 30 diodes. Our price 10 boards 
19.'-. Pima/- P. A P. 



PLEASE NOTE. To avoid any further 
Increased Postal Charges to one Customers 
and enable us to keep our "By Return Postal 
service" which is second to none, we have 
re-organi»ed and streamlined our Despatch 
Order Department and we now- request you 
to send all your orders together with your 
remittance, direct to our Warehouse and 
Despatch Department, postal address: 
BI-PAK SEMICONDUCTORS, Detptteb 
Dept., P.O. BOX 6, WARE, HERTS. Postage 
and packing still 1'- per order. Minimum 
order 10/-. 



SIL 
I'lV 
50 
100 
200 
300 
400 
000 

1100 
sim 
IO00 
1200 



RECTS. 

750m A3 A 
1/- 2/8 
1/3 3 3 
1/0 4/- 
2/3 4 8 
2/8 5 6 
»,'- 81- 
3/3 8/9 
3/6 7/8 
5/- 9 3 
6 8 11 6 



TESTED 

10A30A 
4/3 9 6 

4/6 15'- 

4 8 20 

6 '6 22 - 

7,6 24- 

8/6 30 

9/- 37'- 

11/- 40'- 

12/8 SO- 
15/ - 



TRIACS 
VBOM 2A ti, 
(TO 



6 A 10.4 
(TO- (TO- 
11 6(1) 43) 
100 14,'- 16- 82 6 
200 17/8 SOI- 88,'- 
400 80/- 24/- 36/- 
VBOM = Blocking volt- 
age In either direction. 

LUCAS 35A SIX. RECTS, 
Branded. 400 PIV, 
Special Price, stud type, 
dying lead, 28/6 each, 

UNI JUNCTION 

UT46. Eqvt. 2X2G4ti. 
Eqvt. TIS43. BEX3O0O 
8/6 each, 25-90 5/-, 
100 UP «;-. 

JtPX SILICON PLANAR 
BC107/8/9. 8/- each; 
50-90. I'lOi 100 np, 
1/8 eacn; 1,000 tff, 
1/6 each. Fully tested 
and coded TO-18 ease, 

3rLICON~g IGH~V OL: 

TAGE RECTIFIERS 
10-Anip 3-K.V. (3000 
IM.V.) Stud Type with 
Flying Leads, 16/- each. 



QUALITY-TESTED PAKS 

(I Matched Trans. OC44/46/81 BID 18/- 

20 Red 9p0t AF Trans. PXP 10/- 

18 White Spot HF Trans. PXP 10/- 

B Silicon Rects. 3 A 100-400 PIV 10/- 

2 10 A Silicon Rects. 100 PIV 10/- 

2 OC1 140 Trans. XPX Switching 10/- 

1 12 A SCB 100 PIV . 10/. 

3 SSU. Trans, 23303 PXP 10/- 

3 200 Mc/s SU. Trans. XPX BSY20/27 10/- 

3 iSener Diodes 1W 33 V 6 % To! 10/- 

4 High Current Trans. OC42 Edvt 10/- 

2 Power Transistors 1 OC26 1 OC35 . . . 10/- 

5 Silicon Rects, 400 PIV 2S0aiA 10/- 

4 OC76 Tranaigtors 10/- 

1 Power Trans. OC20 100\' 10/- 

10 OA202 Sil. Diodes Sub-min 10/- 

2 Low Xolse TTans. XPN 2X920' 30 10/- 

1 811. Trail*. XPX VCB 100 ZT80 16/- 

H OA81 DkMles 10/- 

4 OC72 Transistor? 16/- 

4 OC77 Transistors 10/- 

4 Sil, Rects. 400 PIV fiOOm.-V. 16/- 

5 OET884 Trans. Etjvt. OC44. 10/- 

5 OET883 Trans. Kqvt. OC45 10/- 

2 2X708 Sll. Trans. aoOMc.'s XPX 10/- 

3 GT31 LF Low XoUe Germ Trans. 10/- 

6 IX9H «il. Diodes 76 PIV 75mA 10/- 

8 OA95 Germ. Diodes 3ub-min. 1X09 . 10'- 

3 XPN Oerm. Trans. NKT773 Eovt.. , . 10/- 
2 OC22 Power Trans. Oerm 10/- 

2 OC25 Power Trans. Oerm 10/- 

4 AC128 Trans. PXP High Gain 16/- 

4 AC127/128 Comp. pair PXP/XPX . . . 10/- 

fl 2X1307 PXP Switching Trans 10/- 

7 COS2H Oerm. Diodes Eqvt. OA71 , . 10/- 

3 AF11B Type Trans. 10/- 

12 Assorted Oerm. Diodes Marked 10/- 

4 AC126 Oerm. PXP Trans 10/- 

4 Silicon Rects. 100 PIV 750mA 18/- 

3 AF117 Trans 10/- 

7 OC81 Type Trans 10/- 

3 OC171 Trans. 10/- 

5 2X2926 81 i, Epoxy Trans 10/. 

7 OC71 Type Trans. 18/. 

2 2S701 Sll. Trans. Texas 10/- 

1 10 A 600 PIV Sil. Recti. 1S45R .... 10/- 

8 BC108 SSL XPX High Cain Trail*. . . 10/- 

1 2X910 XPX Sil. Trans. VCB 100 10/- 

2 1000 PIV Sll. Rect. 1-5 A R53310 AF 10/- 

3 BSYS6A Sll. Trans. NPX 200Mc/» .. 10/- 

8 OC200 Sll. Trans. 1«/. 

2 GET880 Low Xoise Oerm. Trans. . . . 10/- 

1 AF139 PNP High Freq. Trans 10/- 

3 XPX Tram. 1 8T141 A 2ST140 10/- 

4 Mack's 2 MAT100 & 2MAT120 10/- 

3 Madfa 2 MAT101 * I MAT121 10/- 

4 OC44 Germ. Trans, AF 10/- 

3 AC127 NPX Germ. Trans. 10/- 

i 2X3906 Sll. PXP Trans. Motorola . . . 10/- 

2 Sil. Power Rects. BYZ13 1S/- 

1 Sll. Power Trans. XPX lOOMc/s. 

TK201 A 1(/. 

9 2NI132 PXP Epitaxial Planar Sil. . . 10/- 
» 2X697 Epitaxial Planar Trans. Sll. . . . 15/- 

4 Germ, Power Trans. Euyt. OClfl .... 15/- 

1 Unijunction Trans, 2X2140 16/- 

2 SU. Tram. 200Mc/s (SOVcb ZT83/84 . . 15'- 
20 NET Trans. AF. RF. VHP. Coded + 

Eqvt. List 10/- 

■2 2X2712 Sll. Epoxy Planar HFE225 . . 16/- 

8 BY100 Type Sil. Rects 20/- 

25 Sil, anil Germ. Trans, Mlxeil, all 

marked, Xew 80/- 

SEMI CONDUCTORS FOR "P.E." SO - S0AHP. 
TYPE EACH TYPE EACH 

2X1613 4/8 1X914 l/~ 

2N30S5 IS/8 OA200 1/- 

2N3703 8/- BFY01 S/8 

2X3704 8/6 BYZ13 4 6 

2X3T07 S/8 40362 14/- 

2N3819 8/- SSTllWZenei 3/6 



* CIRO No. 388-7006 



BlfA^ 



High Street 
WARE 






KING OF THE PAKS BIPAK GuaRAHTtE SATlSFftCTlOH Oft MONEY BACK 



Practical Electronics October 1970 



829 






iH;ittH4;i 



MAIL ORDER 
DEPT. 



RADIO LTD. 
HMO MAYES ROAD J]] ill nam 



PSYCHEDELIC LIGHT CONTROL UNIT 

_^-_»- Three Channel: Kitse— Middle— Treble. 

— -^_ Each channel has its own t o n al U vjty 

conlm!. Just connect the input of this 
unit to the loudspeaker terminals of an 
amplifier, and connect three 260Y up to 
500W lamps to the output terminal* 
of the unit, and yon produce ■ fciscinatinK 
Kiminl-Ush! display. (All imaranteedl 
£18.10». Plus 7/8 P. ,v 1'. 
if you require more informal inn please send S, A.K. 




HIGH QUALITY IMPORTED HEADPHONE 
TTC 

G1105 



!.<«'•• I" t l-h,.:.- 

•i.OOfl (J per phone 

Must 2/- P. i 



.. 15 11 
. . 17'8 

pet p*ir 




Q 



CHROME TV STAND 

_'*ju HUil L»J b 1 1 hJgtt, This modem tLsnigrn 
TV BtiHid wmild tsatft jiti IiScaI Ikih*; fur a untTec 



32/6 



SOLID STATE BLOCK MODULES 

Phono pre-n nip E1311: Input, 100K; piin, 28db; 

mni. out, 3-volt; max, in, GQM'V; jKiwer, 9V. 

Tape pre-nmp E1312. a* above. 

M ic. pre-omp F.131 3. a- above. 

Power amplifier E13H: input, l.nuu uhiirs: 

train, 2Mb, SOOM/W; power, 9-vult d.o, 

Electronic orRati, tnnc Me, E1315: tunc freq,. 
iOU-lkHii; output. SOa/W; power, 9V; current, ISM,' A. 
Dual Hasher E13IF: Hasher time. I ! sees; power, BV; current. ISC'M A; 
■lamp, 6V 150M/A. 
tW also stock the mom Dodo practice modules la Ihis range* 




ALL AT 25/" 



I'ln 



BATTERY 
ELIMINATOR 



Ptos viiiir Tianslsto 
Had in, Amplifier, Cas 
sette, etc., into the a.c. natal 
through this compact eliminator. 
SJln-'Jln 3in appros. 4JV 29 6, 
tlV 89/8, !(V 88/8, 7;V complete 
with cable and plug (or Philips 
Cassette. io/JL Plus ■_>/- P. & P. 




,e -»/*sa. a '- 



MAINS TRANSFORMER 

Fused Friinarv 240V. Seeoiiilftrv 
220V at MM/A, MV at 1A. 
This transformer It 
made to n. very high 
standard and is n 
ninallsize: 2in \2iiu 

P li 5- P .I2/6 FlU83 '- 





EMI LOUDSPEAKER 450 

wired 
ever- 
imp. 



10 watts. l.HIll :'. Sin + 1 
t woetCTs .1 ii L ernyst v'. Ml 
and ready for use. This 
jiopular 460. In 3-8-15 ohm i 



65/ 



- pin 



7/fi P. .V P. 




SHELF UNIT 

Two teak finish shelves on a hlnek Jrarue 
(overall aire; 281a :. 26in :•: lain). Ideal for 
hi n equipment: amplifiers, speaker cabinets, 
etc. The perfect answer for housing unit 
audio and equipment. This unit ia wall 
mount incr. 



50/- 



rJiwH.ti p. ,v r. 



CRESCENT CASSETTES 

Top quality cassettes at unbeatable 
pries* b-nnipletc with standard storage 
ease): C60 7/8. 090 18 6. 

012(1 17,8. Plus I,' P, »< P, 



IMPORTED PANEL METERS 



KA-3SC Ijin l'Jll. SOjxA, 
10u,nA, fiOOjuA 1M/A, SMi'A. 
8 i u eter 1 M/ A , 300 V. A 11 at 

plus i; • 

P. A P. 



29/6 



KA-05C 3iin : Sliu 
H meter 60% A, 1M,'A. 

39/6 



300V, 
All at 
Ftoa 1 (8 
p. * p. 



All uioilem design ami iimde to hiuh Htamiards, 



BRITISH RECORDING TAPE 

o( the finest qnahtv (all guaranteed). 13 in OOOIt, 
8,S each. 3 for S4<-. 53 in 900 tt, 10/- each. 
3 for 88/8. Tin 1,20011, 11/8 each. 3 for 38/-. 
Please iaelude 1/8 ras each order lor P. & P. 




COMPONENTS CORNER 

Sin :< Oiu one sided printed circuit board .. 
BY 100 type rectifier BOO p. 1. v. "50M/A 

4 pin translator holders 

"Jiin 80 ohm loudspeaker 

'Jlin 25 ohm .outispeaker uliii 

-Jiin 8 ohm loudspeaker 



8/ - each 
3/3 each 
8d each 
5/8 each 
5/8 each 
8,8 each 



V 2 battery holders (blue plastic) 1/- each 

Flick switches Ijin dullv mains tvpe .3/8 each 

Model motors 0-12 volt , */8 each 

10 ohm W/W pot loudspeaker control E/8 each 

OC81 double heat clips *d each 

Tape recorder rev. counters 6/ -each 

Please include P. it P. 
Send 3,'- for c.mr Componcnl Catalogue and Flog Lists. 



MULLARD "UNILEX" 
NOW IN STOCK 




El'SOOO output iinjdu.e tS.18.0 

EP9001 pre-amp module .. .. £3.8.0 

EP9002 power supply i4.1E.O 

Control panel, asserohlv and cmitohcon 

plate ta.5,0 



These new modules from Multard require only a 
screwdriver to assemble, and are the latest type 
in unit audio. 

Please include 2/0 P. & P. Send S.A.E. for 
further details. 



G. F. MILWARD || MAIL ORDERS: DRAYTON BASSETT, TAMWORTH, STAFFS. 

ELECTRONIC COMPONENTS 

Wholesale/Retail: | 369 Alum Rock Road, Birmingham B8 3DR. Tel. 021-327 2339 



RESISTORS: 

Carbon i/iW 

i/3W 

Wirewound, Multitapped 
1-3W 
5-7W 
10W 
PAPER CONDENSERS: 

TV types, 500V 

Miniature 

ELECTROLYTIC CONDENSERS 

Mains radio/TV types 

Transistor types 

Mixed high/low voltage 
POLYSTYRENE CONDENSERS 
MULLARD POLYESTER CONDENSERS 

SILVER MICA 

WIRE-WOUND PRE-SET SLIDERS 
VOLUME CONTROLS: Double, Mixed 
NUTS AND BOLTS: Mixed lengths/types 

8B.A 

6B.A 

4 B.A 

2 B.A 

METAL SPEAKER GRILLES: 7*In X 3jin 
V.H.F./F.M. TUNERS: Need ECC85 
VEROBOARD: Cutter + 5 2*in >: 1in Bds. 



100 


10/- 


100 


10/- 


10 


10/- 


20 


10/. 


15 


10/- 


10 


10/- 


50 


10/- 


100 


10/- 


to 


10/- 


20 


10/- 


15 


10/- 


100 


10/- 


50 


10/- 


100 


10/- 


15 


10/. 


5 


10/- 


100 


10/- 


100 


10/- 


too 


10/- 


100 


10/- 


6 


10/- 


2 


10/- 




10/- 



TRANSISTORS: 

P.N.P. Untested 

N.P.N 

Light sensitive (OCP71) 

Light sensitive diodes 

OC44 Mullard. 1st grade .. 

OC45 Mullard. 1st grade 

OC22 Mullard. 1st grade 

OC25 Mullard, 1st grade 

2N378 

ASY22 

BY127 Rectifiers 

1 N4007 Rectifiers 

STC3/4 200V 

Unmarked 200V 

Diodes. OA81 

WIRE: 

Solid core, Insulated 

Stranded core, insulated 
SOLAR CELLS: 

Selenium, large, 

small. 

COAX 

Semi air spaced 15 yards 
CRYSTAL TAPE RECORDER MIKES 
EARPIECES 

No plug 

With 2'5mm plug 

With 3-5mm plug 



,. 50 


10/- 


50 


10/- 


5 


«/- 


10 


w- 


4 


10/- 


4 


10/- 


2 


«/- 


2 


10/- 


4 


«/■ 


5 


10/- 


4 


10/- 


4 


10/. 


6 


10/- 


10 


10/- 


40 


10/- 


yards 100 


10/- 


yards 50 


1t/- 


2 


10/- 


3 


10/- 




10/- 


1 


10/> 


6 


«/- 


4 


10/- 


4 


10/. 



FREE I FREE t FREE I ONE PACK EXTRA INCLUDED FREE WITH ORDERS VALUE £5. THREE PACKS EXTRA FOR £10 ORDERS. 
C, F. MILWARD. Drayton Basset*, Tamworth, Staffs. Postage (minimum) per order 2/-. 



830 



Practical Electronics October 1970 



STEPHENS 



ELECTRONICS 
P.O. BOX 26 
AYLESBURY, BUCKS. 



SEND S.A.E. FOR LISTS 

GUARANTEE 

Satisfaction or money 

refunded. 









VALVES 


A-Z3I 


9/6 


EFI84 


M/3 


PUS 


DAF9I 


8/3 


EH90 


10/3 


PL8I 


DAF96 


8/3 


EL34 


9/9 


PL8IA 


DF9I 


9/- 


EL4I 


10/- 


PL82 


DF96 


9/- 


EL8I 


9/6 


PL83 


DK9I 


11/6 


EL84 


7/9 


PL84 


DK96 


11/6 


EL95 


»/- 


PL500 


DL92 


7/6 


EMBI 


11/6 


PL504 


DL94 


7/6 


EM84/7 


12/9 


PL505 


DL96 


9/3 


EYSI 


7/6 


PL50B 


DYB6/7 


8/- 


EY86/7 


7/9 


PL509 


DY802 


8/6 


EX40/I 


7/6 


PL802 


EABC80 


10/6 


EZ30 


6/6 


PL805 


EBC33 


M/- 


EZ8I 


5/9 


PY32 


E8C41 


9/6 


GY50I 


14/6 


PY33 


EBCBI 


6/6 


GZ30 


9/6 


PY8I 


EBC90 


9/6 


GZ32/4 


M/9 


PY800 


EBF80 


8/- 


GZ33/7 


16/3 


PYBOt 


EBF83 


8/- 


KT66 


25/6 


PY82 


EBF89 


«/- 


KT88 


32/6 


PY83 


EB9I 


5/3 


N37 


15/6 


PYB8 


ECC8I 


8/- 


N339 


25/6 


PY500 


ECC82/3 


8/6 


PC86/8 


10/3 


PZ30 


ECCS4/5 


8/6 


PC9Q0 


10/3 


RI9 


ECC88 


M/- 


PC9S 


7/3 


R20 


E88CC 


12/6 


PC97 


8/3 


UABC80 


ECF80/2 


9/6 


PCC84 


9/3 


UBF89 


ECF86 


11/- 


PCC8S 


8/6 


U8C4I 


ECH3S 


13/6 


PCC88 


14/- 


UCC8S 


ECH42 


13/3 


PCC89 


12/3 


UCH42 


ECH81 


10/3 


PCCI89 


12/3 


UCHBI 


ECH83 


8/- 


PCF80 


10/3 


UCL82 


ECH84 


9/6 


PCFB2 


10/6 


UCL.83 


ECLL80C 


20/- 


PCF84 


9/6 


UF4I/2 


ECL80 


8/- 


PCF86 


12/3 


UF80/5 


ECLB2 


9/9 


PCF200/ 


16/3 


UF89 


ECL83 


11/6 


PCF80I 


12/3 


UL4I 


ECLB6 


9/9 


PCF802 


12/3 


UL84 


EF39 


10/6 


PCF805 


13/- 


UM80/4 


EF8D 


8/- 


PCF806 


12/3 


UY4I 


EF83 


10/- 


PCF808 


13/6 


UY8S 


EF85 


8/3 


PCHZOO 


11/6 


U25 


EF86 


13/3 


PCLB2 


10/3 


U26 


EF89 


B/- 


PCL83 


12/3 


UI9! 


EF9I 


8/6 


PCL84 


10/3 


UI93 


EF92 


10/- 


PCL85 


10/6 


U30I 


EF93 


9/6 


PCL86 


10/3 


W729 


EF94 


15/6 


PDSOO 


30/6 


Z759 


EF9S 


12/6 


PFL200 


14/9 


5Y3 


EFI83 


11/3 


Pt-36 


12/9 


5Z4 



18/- 
10/3 
12/6 
7/3 
10/3 
8/3 
16/6 
17/- 
29/- 
20/- 
30/9 
17/3 
17/3 
10/- 
10/9 
8/3 
8/3 
8/3 

, 7 '- 
10/- 

8/3 

20/- 

16/- 

13/- 

15/- 

10/6 

8/- 

9/9 

9/3 

13/9 

10/9 

10/3 

12/3 

% 

8/3 
11/6 
11/- 
9/- 
8/- 
6/9 
15/- 
15/- 
14/6 
8/3 
17- 
II 

24/6 
8/6 
9/6 



6U4 
6AT6 

6U6A 

6AV6 

6BA6 

6BE6 

6BR7 

6BF.8 

6BW6 

6BW7 

6CD6G 

6V6G 

6X4 

6X5 

I2AU6 

I2BA6 

I2BE6 

I2BH7 

3SW4 

S0C5 

6F23 

6F24/5 

6F26 

6F28 

6/30L2 

I0FI 

I0FI8 

I0P13 

I0PI4 

20 P4 

30CI 

30CI5 

30CI7 

30CI8 

30F5 

30FLI 

30FL i 2 

30FLI4 

30LI 

30LI5 

30LI7 

30PI2 

30PLI 

30P4MR 

30PI9 

30PLI3 

30PLI4 

30PL15 



15/- 

9/9 

(5/6 

6/6 

9/6 

12/- 

15/- 

19/- 

16/6 

13/9 

28/- 

8/- 

7/6 

9/6 

15/- 

9/6 

12/- 

14/- 

9/6 

12/6 

15/6 

12/6 

8/3 

11/6 

15/6 

15/- 

10/- 

16/- 

19/- 

20/- 

10/3 

1 3/9 

15/9 

13/6 

16/6 

12/9 

17/6 

13/6 

9/3 

IS/3 

14/6 

15/6 

12/9 

20/- 

12/9 

IB/6 

18/6 

18/6 



90% B.V.A. BOXED (NORMAL GUARANTEE) OR OWN 
VALVES SUPPLIED, I YEAR'S GUARANTEE. ADD 6d PER 
VALVE ON ORDERS UNDER 6, OTHERWISE FREE POST 
AND PACKING. 



SEMICONDUCTORS 



ACII7 


12/- 


BCII5 


6/6 


AC 126 


4/4 


BCII7 


7/9 


AC 127 


4/9 


sens 


7/9 


AC 128 


4/6 


BCI34 


11/6 


AC 176 


7/4 


BC147 


5/8 


ACYI7 


6/- 


BCI48 


4/4 


ACY20 


6/- 


BCI52 


5/6 


AD 149 


11:8 


BCI75 


S/6 


ADI6I 


6/9 


BCI87 


5/8 


ADI62 


6/9 


BC2I3L 


5/4 


AFII4 


4/8 


BDY20 


30/6 


AFII5 


4/8 


BFYSO 


5/- 


AFII6 


4/9 


BFX84 


7/- 


AFII7 


4/6 


BFX29 


7/6 


AF1I8 


12/- 


BFII5 


5/6 


AFI26 


4/8 


BFII7 


9/6 


AFI27 


4/8 


BFI63 


V- 


AFI39 


8/8 


BFI67 


*/- 


AFI78 


9/- 


BFI73 


7/- 


AFI79 


9/- 


BFI78 


7/- 


AFI80 


12/4 


BFI80 


8/- 


AFISl 


9/4 


BFI8I 


8/- 


AFI86 


13/4 


BFI82 


B/- 


AF239 


8/6 


BFI84 


5/- 


BC107A 


5/- 


BFJ94 


5/- 


BCI03B 


4/6 


BFI97 


6/4 


BCI09C 


5/- 


BF200 


7/4 


BCII3 


5/6 


BF224 


«/- 



BF225 
BF257 
BF22A 

NKTI2S 

NKT281 

NKT40I 

OC25 

OC44 

OC45 

OC7I 

OC72 

OC77 

OC78 

OC8I 

OC8ID 

(GETN3) 

OC84 

OCI69 

OCI7I 

QC200 

OC202 

OC203 

OCP7I 

P346A 

2N456A 

2N697 

2N69B 

2NII32 



6/- 
9/6 

9/6 
5/9 
4/- 
17/6 
9/6 
5/6 
S/4 
4/4 
5/4 
5/6 
51- 
47- 
4/- 

5/- 
4/8 
6/- 
6/6 
9/6 
6/6 
12/6 
4/6 
17/6 
5/10 
10/6 
11/6 



2NI305 
2NI306 
2N305S 
2N3392 
2N3702 
2N370S 
2N37II 
2N38I9 
2N3826 
2N4062 
2N4289 



4/10 
6/2 
15/- 

5/- 
5/6 
4/6 
4/9 

9/- 
«/- 
4/6 
4/6 



RECTIFIERS 

BY 126 4/4 

BY 127 5/- 



DIODES 

AAII9 

OA47 

OA79 
OA8I 
OA9I 
OA202 

BZY88 
(SERIES) 



V- 

1/9 

1/10 

1/10 

11- 
lf- 

6/6 



CATHODE RAY TUBES 

New and Budget tubes made by the leading Britrsh manufacturers 
Guaranteed for 2 years. In the event of failure under guarantee, replace- 
ment is made without the usual time wasting forms and postage expense. 



ADD 5d. PER ITEM FOR POST AND PACKING 
FOR ORDERS UNDER 24 PIECES. 



Type 

MW36-20 
MW36-2I 
MW43-69Z 

MW43-80Z 
AW43-80Z 



AW43-88 
AW47-90 
AW47-9I 
A47-I4W 



A47-I3W 

A47-IIW 

A47-26W 

A47-26W/R 

A50-I20W/R 

AWS3-80 

AW53-88 

AW59-90 

AW59-9I 

A59-ISW 



AS9-IIW 

AS9-I3W 

A59-I6W 

A59-23W 

A59-23W/R 

PORTABLE SET TUBES 

TSD2I7 

TSD282 

A28-I4W 

CMEI601 

CMEI602 



CRMI71 
CRMI72 
CRMI73 
C ME 1702 

CMEI7Q3 

CMET706 

CI7AA 

CI7AF 

CMEI705 

A47-I4W 

CME190I 

CMEI902 

CMEI903 

CI9AH 

CMFJ906 

CMEI90S 

CMEI905 

CMEI9I3R 

CME20I3 

CME210I 

CME2303 
CME230I 
CME2302 
CME2303 
CME230S 
CME2306 
CME23Q6 
CME230S 



New 



6.12.0 
6.12.0 
6.12.0 
6.12.0 
6.12.0 
6.12.0 
6.12.0 
6.12.0 

7.13.4 
7.13.4 
7.13.4 
7.13.4 
7.13.4 

10. 5.6 
8.17.3 
8.17.3 
9. 6.8 

10.17.0 
8.18.8 
6.18.8 

9.11.8 



9.11.8 

13.13.0 
13.13.0 
12.12.0 
12.12.0 



9. 3.4 



Budget 
C 
4.10.0 
4.10.0 

4.12.6 
4.12.6 
4.12.6 
4.12.6 
4.12.6 
4.12.6 
4.12.6 
4.12.6 

5. 7.6 
5. 7.6 

5. 7.6 
5. 7.6 
5. 7.6 

S.IO.O 
7. 0.0 
7.15.0 



5.0 
5,0 



7. 4.0 



7. 4.0 

10.19.6 
10.19.6 
1 0.1 0.0 

1 0.1 0.0 



6.15.0 
6.15.0 
Not supplied 
7.15.0 
8. 0.0 



A discount of 10% is also given for the purchase of 3 or more New tubes 
at any one time. 
All types of tubes in stock. Carriage and insurance 15/-. 

TRANSISTORISED 
UHF TUNER UNITS 

NEW AND GUARANTEED 
FOR 3 MONTHS 

Complete with Aeriai Socket and wires for Radio and Allied TV sets but 

can be used for most makes. 

Continuous Tuning, 90/-; Push Button, 100/-. 

STYLII 

TC8, GC2, GPS9, GC8, DC284, Stereo I OS, 106, 208, 2/- each (individually 
boxed); ST3/5, ST8/9, 9TA, 9TA/HC, GP9I, 8/-, Diamond. Post and 
packing Sd per item for orders under 24. 

TAPES (Polyester PVC) 

4in LP., 8/6; 3in L.P., 5/6. 

Standard Play: 600ft Sin, 8/6; 900ft 5}in, 10/6; 1,200ft 7in, 12/6. 

Long Play: 900ft Sin, 11/-; 1,200ft 5} in, 13/-; 1,800ft 7!n, 18/-. 

Double Play: i, 200ft Sin, 16/- j 1,800ft 5 Jin. 19/-; 2,400ft 7in, 28/-. 

Philips type Cassettes (in plastic library pack): C60, 10/6; C90, 12/6; 

CI20, 19 6. 

Post and packing 1/6 on all orders. 

ACOS CARTRIDGES 

GP91-I — Medium output Mono Crystal, 21/- inc. P. Tax. 

GP9l-3sc— High output Mono Crystal (TC8H, TCBM, BSR X3H. X3M). 

21/- inc. P. Tax. 
GP93-I -Stereophonic Crystal, 24/9 inc. P. Tax. 
GP94-I — Stereophonic Ceramic, 31/- inc. P. Tax, 
GP95-I — Stereophonic Crystal, 24/9 inc. P. Tax. 
GP96/I— Stereophonic Ceramic, 31/6 inc. P. Tax. 



TERMS, CASH WITH ORDER ONLY. POST AND 
PACKING PAYABLE ON ORDERS UP TO £3, 
AFTER THAT, FREE EXCEPT C.R.T.'s. 



Practical Electronics October 1970 



831 



R.S.T. VALVE MAIL ORDER CO. 

BLACKWOOD HALL, WELLFIELD RD., S.W.16 
SPECIAL EXPRESS MAIL ORDER SERVICE 



]N21 

iNaiB 

1N23 

1N85 

LN263 

1NM6 

IN 645 

1N72SA 

1X4UI.iT 

IS OS] 

18113 

IS 130 

18131 

2G220 

2G240 

2G301 

2G306 

20371B 

2G381A 

2G403 

2G414 

HG417 

2N2U 

2X101 

2N247 

2N897 

2S698 

2N706 

2N706A 

2N70B 

2N709 

2N7U 

2N987 

2N1060 

2HIG91 

2K1131 

2S1132 

2N1S02 

2N1303 

2N1304 

2N130S 

2N1306 

2X1307 

2N13Q8 

2N1309 

2X1420 

2X1607 

2N1S26 

2X1909 

2X2147 

2X2144 

2X2190 

2X2X93 

2X2287 

2X2297 

2X2369 A 

2S2410 

2X2411 

2X2412 

2X2483 

2N24S4 

2X2846 

2N2698 

2X2865 

2X2904 

2X2904 A 

2N2906 

2X2907 

2N2928 

2H2924 

2X3014 

2X3054 

2N305S 

2X3705 

2X3700 

2X3707 

2X3708 

2X3709 

2X3710 

2S3S19 

2X3820 

2X3823 

2X3900 

2X3900A 

2S5027 

JNSOSC 

2X5307 

2X5308 

2X5309 

28006 

28013 

2S013A 

28301 

28304 



AF1J6 
AF117 
AF118 
AF119 

AF124 



7^6 BCY31 
7/8 . BCY32 
U/- I BCY33 
14/- I BCY34 
16/- I BCY38 
Hi. 6 BCY39 
12/8 ■ BCY40 
9— BCY42 



6/6 
13/6 
7/3 
7/6 
19/8 
19/6 
3/6 
3/6 



19/6 

8/3 
8/3 



GET116 

OET118 

GET119 

GET 120 

GET687 

GET872B 6/- 

(.!ET*73 

GET875 

GETSSO 

GET882 

GET 885 10/- 

GEX35 4/6 

GEX44 

GEX94I 

GJ3M 

GJ4M 

GJ5M 

HG1005 

MAT 100 

MAT101 

MAT120 

MAT121 

MJ420 

MJ421 

XKT128 

NKT129 

XKT136 

XKT210 

XKT211 

NKT212 

XKT213 

XKT214 

NKT215 

KKT218 

XKT217 



«/- 
4/- 
41- 
6/6 
8/8 



6/- 
8/9 
«/- 



1/6 

4/- 
7/6 
7/6 
7/6 
10/- 
6/- 
8/3 
B/ 9 
6/- 
22/- 
22;'- 



v- 

5 fS 

6,- 

Sjfl 

5:-) 

m 

4. '4 

4, fa 
t i 

£.4 



SKT218 22,'fi 



XKT219 
XKT221 
XKT223 
X KT224 
XKT226 
XKT227 
XKT-229 
X KT237 
XKT238 
XKT240 
XKT241 
XKT261 
XKTS61 
XKT-274 
SKT275 

XKT403 
NKT404 12/6 
NKT678 6/- 
XKT713 
XKT773 
XKT777 



7/6 
«/- 

t a 

20/- 
7/6 

3;'S 

3(- 

2/- 

] 6 

a/- 
»■> 

i:- 
1/8 
1/6 

in 

*h 
i a 

i 1 

1/6 



XKT80113 

078B 

OA5 

OAJO 

OA47 

OA70 

OA71 

GA73 

OA74 

OA79 

OA81 

OA86 

OASS 

OA90 

OA91 

OA95 

OA200 

OA202 

OA210 6/6 

OA211 10/- 

OAZ200 11/- 

OAZ201 10/ 

OAZ202 

OAZ203 

OAZ204 

OAZ207 

OAZ20S 

OAZ210 

OAZ222 

OAZ224 

OAZ241 

OAZ242 

OAZ246 

MZ'»,m 

ocia 

OC16T 
OC19 



7/6 

8/- 
8,<- 
10/- 
6/6 
6/6 
9/6 
9/6 
7/6 
4/6 
4/6 
9/- 
15/- 
16/6 
8/8 



OC20 
OC22 
OC23 
OC24 
OC26 
OC26 
OC28 
OC29 
OC30 
OC35 
OC36 
OC38 
OC41 
OC42 
OC43 
OC44 
OC45 
OC48 
OC68 
OC59 
OC70 
OC71 
OC72 
OC73 
OC74 
OCTfi 
OC76 
OC77 
OC7B 
OC78D 
OC79 
OC81 
OC81D 
OCS1DM 3/- 
OC81M B/- 
3/- 



20/- 
8/- 
8/6 
»/- 
7/6 
8/- 
12/6 
14/6 
8/- 
6/3 
8/6 
10/3 
4/6 
61- 
91- 
4/- 
3/3 
V- 
12/6 
17/- 
3/6 
3/- 
*!' 
7/3 
4/3 
4/6 
3/- 
8/- 
3/- 
3/3 
61- 
4/- 
3/- 



OC82 

OC82D 

OC83 

OCS4 

OC114 

OC122 

OC123 

Of 1 39 

OC140 

OC141 

OC169 

OC170 

OC171 

OC172 

OC200 

OC201 

OC202 
, OC203 

OC204 

OC205 

OC206 

OC207 

OC4S0 

OC470 

OCF71 

PS144 

819T 

8AC40 

SFT30B 

SJ052F 

ST722A 

8T7231 

BX6B 

SX68UH 4/6 

9X631 7/6. 

8X631UC 10/- 

SX680T 4/- 

8X634WK 8/- 

SX753 15/- 

SZ33C 12/- 

V16/10F 16(- 

V16/30P Ifi/- 

V 30/20 IP 9/8 

XA122 8/- 

, XA124 
I XA142 

XA143 

XA162 
1 XA162 

XB101 

XB121 

XK505 

XK618 



4/6 
4/9 
7/8 

12/6 
4/4 
7/6 
8/6 

12/3 
6/- 
6/6 
6/- 
7/- 
6/6 
8/6 
8/6 
6/- 
5/8 
»/- 

14/6 
7/6 
81- 
81- 

20/- 
4/- 
8/- 
6/- 
7/6 
7/8 
6/- 

12/6 
*/■ 



Z2AS2CH 6/- 
ZB24 12/0 

ZS32A 8/- 

ZT21 «/- 

ZT43 6/- 



TRANS1STORS (POSTAGE, PACKING & INSURANCE) l/J PER ORDER 



SEND S.A.E. FOR LIST OF 3,000 TYPES- 
VALVES, TUBES AND TRANSISTORS 



TERMS OPEN DAILY TO CALLERS 

C.W.O, ! Mon,-S»e,9a.m,-5.30p.m. Closed Sit. 1.30 p.m. -1.30 p.m. 
noC.O.D. Tel. 01-749 0199/1649 




Colbert Pana-Vise work positioners are specifically desiflned 
to quickly and easily achieve the most convenient, comfortable 
and time-saving work position, 

Available with vacuum clamp or screw-on base. 

They can be rotated, tipped, tilted, angled, elevated, 
lowered. 

The required work position is firmly secured with a patented 
one-knob control, a unique feature of Colbert Positioners. 

A series of special holders is available for various types of 
work. 

Full details available on request. 

Distributors i 

SPECIAL PRODUCTS DISTRIBUTORS LTD. 

81 Piccadilly. London, W.I. Tel. 01-629 95S6 Cables: Speciprod London 
(Made in U.S.A.) 




Let us give you the facts 

rrom cover to cover Goodmans Manual ts packed with fascinating 
articles on Stereo; a beginners guide to High Fidelity: Stage- built 
Systems: complete details of Goodmans High Fidelity Audio products. 
28 pages you can't afford to miss . . . and it's yours FREE I 



Please send me a free copy 



Name 

Address 



Goodmans Loudspeakers Limited 

Axiom Works, Wembley, Middlesex. Tel : 01 -902 1 200 P.E.I0 



832 



Practical Electronics October 1970 






LIMITED 



FULLY TESTED AND MARKED 



AC 1 07 

AC 1 26 

AC 1 27 

ACI2B 

AC 1 76 

ACYI7 

AF239 

AFIB6 

AFI39 

BCIS4 

BC17I = BC107 

BCI72 = 3CI08 

BFI94 

BF274 

BFY50 

BSY25 

BSY26 

BSY27 

BSY2B 

BSY29 

BSY9SA 

OC4i 

OC44 

OC4S 

OC71 

OC72 

OC73 

OCB1 

OCBID 

OCB3 

OCI39 

OCI40 



3,- 
2^6 

3/6 
2,6 
5/- 
3'- 
12/6 
10/- 
10,'- 

s/- 

2/6 
2/6 
3 - 
It- 
4j- 
7,6 
2/6 
2/6 
2 '6 
2/6 
3/- 
2/6 
2/6 
2/6 
2/6 
2/6 
3/6 
2/6 
2/6 
4/- 
2/6 
3/6 



OCI70 

OCf7l 

OC200 

OC201 

2G30I 

2G303 

2N7II 

2N 1 302-3 

2N 1 304-5 

IN I 306-7 

2NI30B-9 

2N38I9FET 

Power 

Transistors 

OC20 

OC23 

OC2S 

OC26 

OC2B 

OC35 

OC3G 

AD 149 

AUYIO 

2S034 

2N3055 

Diodes 

AAY42 

OA95 

OA79 

OAB1 

IN9I4 



4/6 
4/6 

5/- 
5/- 
2/6 
2/6 
10 - 
4,'- 
5,'- 
6/- 
Fj- 
9/- 



10/- 

61- 
5/- 
51- 

s;- 

5,'- 
7,6 
6/- 

25,'- 
5/- 

12/6 

V- 

21- 
1/9 
1/9 
1/6 



FREE! 

PACKS OF YOUR OWN CHOICE UP TO 
THE VALUE OF 10/- WITH ORDERS 
OVER £4 



SURPLUS INTEGRATED CIRCUITS 



These are brand new genuine surplus Stocks* 
marked Add guiranteed to full makers" specification 
and not re-marked rejects. 



W 



NE808A 

NE9I6A 

NE825A 

NEB40A 

NE8SSA 

NEB70A 

SN7430 

SP6I6A 

SP63IA 

SP670A 

SP806A 

SP808A 

SP8I6A 

SP82SA 

SP840A 

SP9SSA 

SP870A 

SP880A 

NE500K 

NB50IK 

NE806J 

NEB08J 

NE8I6J 

NE82SJ 

NES40J 

N E8S5J 

ST620A 

ST6S9A 



Suffix 
pack- 



Price 
Single 8 l/P Nand Gate TTL 7/- 

Dual 4 l/P Nand Gate TTL 71- 

D.C. Clocked 1-K. Rip-Flop TTL 17/6 
Dual 4 l/P Exclusive OR Gate TTL 71- 
Dual 4 Power Gate TTL 7/- 

Triple 3 l/P Nand TTL 7/- 

8 Input Positive Nand Gate TTL 7\- 
Dual 4 Nanc Gate DTL 71- 

Quad 2 t/P Gate Expander DTL 
Triple 3 Nand Gate TTL 
Dual l/P Expander TTL 
Single 8 l/P Nand Gate TTL 
Dual 4 l/P Nand Gate TTL 
D.C. Clocked J-K Ftip-Flop TTL 
Dual 4 l/P Exclusive OR Gate TTL 71- 
Dual 4 Power Gate TTL 
Triple 3 l/P Nand TTL 
Quad 2 l/P Nand TTL 
Video Amplifier 
Video Amplifier 40MHz 
Dual 4 l/P Expander TTL 
Single 8 l/P Nand Gate TTL 
Dual 4 l/P Nand Gate TTL 
D.C. Clocked J-K Ffip-Flop TTL 17/6 
Dual 4 l/P Exclusive OR Gate TTL 7/- 
Dual 4 Power Driver TTL 7/- 

J-K Hip-Flop DTL 17/6 

Dual 4 Buffer/Driver DTL 7/- 



DIPI4lead:K = l0leadTO5;J 



7:- 

Th 

71- 

7 - 

7i- 

17/6 



71- 
71- 
40/- 
40/- 
71- 
7/- 
71- 



NEW TESTED AND GUARANT EED PARS 

JO/- 
10/- 



B2 

B77~ 

mT 

B9I 



A Photo Cells, Sun Batteries. 
^ 0-3 to 5V, OS to 2mA. 

2ADI6I-ADI62 NPN/PNP 
Trans. Comp. Output. Pair 



10 



Reed Switches, 
large and small 



5SP5 Light Sensitive Cell*. 
Light Res. 400 fi Dark I M ft 



IQj- 

10- 



NKTI63/I64 PNP Germ. TO-S 
equivalent to OC44. OC45 



NPN, Si I. Trans. A06- 
BSX20, 2N2369 500 MHi. 
360mW 



10/- 

10- 



B93 
B96 



GETI 13 Trans, equiv. t 
ACY 17-21 PNP Germ. 



2N3I36 PNP Sil. Trans. 
TO- 1 8, HFE 100-300 I.C. 
600mA. 200 MHi 



10/- 



10 



XBII2and XBIC'2 equiv. 
AC 1 26, AC 1 56, OC8I/2, 
OC7|.'2, NKT27I, etc. 



H4 

H7~ 
HF 
H9~ 



250 



Mixed Resistors- 
Packing^- 



10/- 

W- 



40 



Wirewound Resistors, Mixed 
types 3nd values. Postage 1/6 



BY 1 27 Si I, Rets 

1000 PIV. I amp. plastic 



_I0/- 
10/- 



LOOK ! TRANSISTORS ONLY 6d EACH 



TYPE A 

PNP SILICON ALLOY 

TO-5 CAN 
"SPEC:- 

ICER AT VCE = 20v 
ImA MAX, 
HFE 15-100 

THESE ARE OF THE 2S300 
TYPE WHICH IS A DIRECT 
EQUIVALENT TO THE 
OC200..20S RANGE 



TYPE B 

PNP SILICON PLASTIC 

ENCAPSULATION 
SPEC:- 

ICER AT VCE-, I0v 
ImA MAX 
HFE 10-200 

THESE ARE OF THE 
2N3702/3 AND 2N4059/62 
RANGE 



TYPE E 

PNP GERMANIUM FULLY 
MARKED AND TESTED. 

AF, or RF. 

PLEASE STATE 

ON ORDER 






NEW UNMARKED UNTESTED PftKS 

B80 ft Dual Trans. Matched O/P I A ; 

** pairs NPN. Sil. in TO-5 can ■ v ! 




RETURN OF THE UNBEATABLE P.I PAR. 
NOW GREATER VALUE THAN EVER 

FULL OF SHORT LEAD SEMICONDUCTORS 
AND ELECTRONIC COMPONENTS. APPROX. 
170. WE GUARANTEE AT LEAST 30 REALLY 
HIGH QUALITY FACTORY MARKED TRAN- 
SISTORS PNP AND NPN. AND A HOST OF 
DIODES AND RECTIFIERS MOUNTED ON 
PRINTED CIRCUIT PANELS. IDENTIFICATION 
CHART SUPPLIED TO GIVE SOME IN FORMA- 
TION ON THE TRANSISTORS. 

PLEASE ASK FOR PAK P.I ONLY 10/- 
2/- P. & P. on this Pak. 



Make a Rev. Counter for your Car. The 

'TACHO BLOCK'. This encapsulated block 
will turn any Q-1mA meter into a linear 
and accurate rev. 
counter for any car. 



200 



Trans, manufacturer's rejects 
all types NPN, PNP, Sil, and 
Germ, 



[00 



Silicon Diodes DO-7 glass 
equiv. to OA200. OA202 



10/- 



50 



Sil, Diodes sub. min. 
IN9I4 and IN9I6 types 



50 



Sil. Trans. NPN, PNP, 
equiv. to OC200/I, 
2N706A, BSY9SA, etc. 



10 



7 Watt Zener Diodes 
Mixed Voltages 



40 



250mW. Zener Diodes 
DO-7 Min. Glass Type 



25 



12|6 Each 



Mixed volts, I i 
Top hat type 



30 



MAT Series "alloy** pnp 
Transistors 



JO/- 

10/- 

to~- 
W- 

I0/- 



. sv Packing 
Post » " 



10 



* M 




Experimenters' Pak of 
Integrated Circuits. Data 
supplied, 



I0- 



7Q BYl26/7Type Silicon 
* u Rectifiers, I amp plastic, 
Mix±d volts 



I0,<- 



20/- each 



FREE CATALOGUE AND LISTS 

for: — 

ZENER DIODES 
TRANSISTORS, RECTIFIERS 

FULL PRE-PAK LISTS 
& SUBSTITUTION CHART 



MINIMUM ORDER 10/- CASH WITH 
ORDER PLEASE. Add 1/- post and packing 
per order. OVERSEAS ADD EXTRA FOR 

AIRMAIL. 



P.O. RELAYS 

Various Contacts and Coil 
Resistances, No individual 
selection. Post & Packing 5/- 



8 FOR 

20/- 



4Tte 



FREE! A WRITTEN GUARANTEE WITH ALL OUR TESTED SEMICONDUCTORS 



BIPREPAK LTD 



DEPT. A, 222-224 WEST ROAD, WESTCLIFF-ON-SEA, ESSEX 
TELEPHONE: SOUTHEND (0702) 46344 



Practical Electronics October 1 970 



833 



EVERYTHING BRAND NEW AND TO SPECIFICATION • LARGE STOCKS 



BARGAINS IN NEW SEMICONDUCTORS 



1NB14 

1S3754 

15T414H 

1N5054 

1S940 

2N696 

2SJ607 

2N706 

2X1302 

2X1303 

2X1304 

25)1305 

2X1306 

2X1307 

25130S 

2X130!! 

2X16 13 

2X1711 

2X2147 

2X22] fl 

2X2270 

2X2484 

2X26 4G 

2X2904 

2X2924 

2X2926 

2X2921'. 

2X306:1 

2X3054 

2X30 5 j 

2K33-;. 

2S3S63 

2X3TU-J 

2X370!) 

2X3704 

2X3705 



2X37Dii 
2X3707 
2X370S 
2X37 0J» 
2X3710 
5 6 2X3711 
5/8 2X37 3 J 
£9 2X3794 
i,<- 2X3819 
4/- 2X3820 
4 6 i 2X3904 



1/3 

lit 
4,'- 



2X3906 

■jX4o;.s 

2X4059 

2N406O 

2X4061 

, 2X4062 

7/_ I 2X4284 

18/1 2X4286 



9/3 

lit 

18/8 
10/9 
11/- 
4/- 
4,6 
2 '3 

s/e 

14/3 

un- 
ion 

ll/S 
3/8 

3/3 
3 9 
3S 



2X428!t 

2X4291 

2X429*2 

2X4410 

2X5062 

2X5163 

2X5192 

2N5195 

2X5457 

2X54u« 

2X544H 

40250 

10361 

40362 

40406 

40408 

40430 



All power ty 

3/3 
4/- 
8/- 
8/- 
38 
3/11 

w/- 

3/3 
8/6 

zse 

7/6 

m 

S3 

n- 

4'3 
4/8 

4 3 

3/3 
3/3 
3/3 
3/3 
3/3 
4/8 
12/8 

a- 
m- 

23/3 

8/9 

99 

9 9 

14/8 

12/6 

18/- 

163 

14/8 

87/- 



pes supplied with free insulating sets 



40512 

40602 

AC 107 

AC 126 

AC 127 

AC 12 8 

AC176 

ACY22 

ACY40 

AOY41 

AD142 

AD149 

ADK.I/AD16: 

(matched) 16/- pr 
AF114 



45/8 I BC147 
9/6 I BC148 

14/6 BC149 
6 6 BC153 



API 15 
AF116 
AK117 
AF124 

AF127 
AF139 
AF180 
AF239 
ASY26 
ASY27 
ASY2S 
B0041 
BA102 
BA156 
BA130 
BA145 
BC107 
BC10H 
BC109 
BC125 
BC126 



BC154 
BC157 
BC16N 
BC15W 
BC167 
BC168 
BC169 
BC177 
BC178 
BC179 
7 BC182L 
7/- BC183L 
" BC184L 
BC186 
BC212L 
UC213L 
BC214I, 
18/6 BCY70 

9/9 | is nrji 

BD123 
BD124 

BFI67 
BF178 
BF160 
BF194 
BF195 
6/8 BFX2S 
2.9 BKX84 
8/8 BFX85 
Z 9 BFX87 
12/- ' BFX88 
18/- : BFY50 



8/3 
8/6 
IS/- 
91- 
41- 



3/8 BFY51 
3/3 B9X 20 
3 8 ' BY164 
BY238 
C106B1 
MCI 40 
MJ480 
M,l4-i: 
MJ491 
MPF102 
XKT403 
.. NKT405 

S I OA47 

'" ' OA90 
OA91 
0A95 
OA99 



19: 

tu- 
rn 

3/6 
3/9 
3/8 

8/3 

s/e 

8/8 



4/8 
2/8 
2 6 ( 

f ',* ' OA200 
| _ OA202 

SB ocn 
|| TIP31A 

18/_ TIP32A 
24J3 T1S43 
ML I ZTX300 
8/8 2TX301 
10/6 I ZTX302 
is/- I ZTX303 
7/_ ZTX304 
7/6 ZTX.50O 
1919 ZTX501 
7/6 ZTX602 
8/8 ZTX503 
8/6 ZTX504 
6/9 ZTX630 
4/6 ZTX531 



4/3 
3 9 
10/- 
3/8 

14/8 
5/- 
21/- 

27/- 
307- 
7/6 
18/6 
16/- 
1/9 
1/3 
1(8 
1/3 
3/- 
1 11 
2/- 
5/6 
17/6 
23 8 
10/6 
3 6 
3/8 
4/8 
4/8 
89 
67- 
6/- 
6/- 
S/- 
12/- 
S/S 
6/6 



RESISTORS 



c 


1/20W 


c 


tw 


c 


iW 


c 


JW 


c 


IW 


MO 


•w 


WW 


IW 


WW 


3W 



10% 
5% 
10% 

2"., 
10% : 



i/20 a 



Yiloci 

Range »v»iUble 1 to S 19 to 99 100 op 

lee note Mow] 

82 Q -220k Q E12 18d 184 15d 

4 7ll-330kO K24 2 id 2d 1-764 

4 70-lOMtl E12 8M 24 1-764 

4-7Q-10MI! B24 3d 2 5d 2254 

4-7Q-10MQ B12 6d Sd 4 5d 

10O-1MO B24 M 8d 74 

0"JO Q-3-90 E12 15d all quantities 

1211-lOkn E12 164 all quantities 

lan-lOkfl F.12 184 all quantities 



unfa*. MO metal oxide ElecLmsit Til5 ultra k.w noise. WW 

E24 denotes series: 



WW 7W 5% 

CODES: = carbon Bin) high stabiltt 

VtJJJEts'ltvi denote! series: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 and their dec-ad 
plus 11, 13, 16, 20, 24, 30, 36, 43, 51 , 62, 75, 91 and their decades. 
Price* are inpente each for same ohmte fnlue and power rating, 
XQT mixed >'nhtrt. {Ignore frartlen* of Id on fotnt reitatar 
order. > 



INTEGRATED CIRCUIT AMPLIFIERS 

SINCLAIR IC10 complete with inatruct inti inmk giving 
amplirlerclrcuit details and range of applications^ 59/6 nett. 

PLE8SEY 8L403A. Only 48/6 each. 3W into 7 8n tor ]8V 
finpplj\ Application data witli two or more* 



WAVECHANGE SWITCHES LONG SPINDLES 
IP 12W; 2P 6W; 3P 4W; 4P 3W 

SLIDER SWITCHES I' I'D. T 



NEON INDICATOR LAMPS all 200/250V 
Square bezel, red only . . . * . . 3/9 

Round chrome bezel red, ;unber. clear , . . , 4/9 each 

Toggle switches, 250V a,c. 1'5A. thronie dolly and 
chrome milled nutS.P.S.T. 3/9; .h.1>,D,T.4/8; D.V.V.T. 5/9; 
S.P.D.T. centre off St-. 



8-DeC'i )>ul an end to "birdsnesting". Components just 
plug it). Kaves valuable time. Vsc components again and 
again. H-DeC only 30/-, Coinnaet T-DeC, 

Increased capacity, may be tern nerature-cye led. T-DeC 
only 50/- post tree. Full range stocked. 



MULLARD POLYESTER C280 tcriM 
260V 20%: 001, 0022, 0033, 0047, 3d ea.; 0068, 01, 
04 ea.; 0-15, 114; 0-22, 1/-. 10%: 0-33. l/6;0>47, 1/8; 
0-68, 2/3: IjuF, 2/9; J-g>F,4.'8; 2-2/jF, if*. 

MULLARD SUB-MIN ELECTROLYTIC 

C426 range axial lead 1/8 each 

Values (uF/V): 0-64/64, 1/40, 16/26, 2-5/16, 2-0/64, 4/10, 
4/40. 5/64, 6-4-'6-4, 6-4/25, 8/4, 8/4U, 10/2-a. 10/16, 10/64, 
12-5/25, 16-40. 20/16. 20/16, 20/64, 25/6-4, 25/25. 32/4, 
32/10, 32/40. 32/64, 40/16. 40/2-5, Ofl.6-4. 50/25, 50/40, 64/4, 
64/10, 80/2-5, 80/16, 80/25, iOO/6-4, 125/4, 125/10, 125/16, 
160/2-5, 200/6-4, 200/10, 250/4, 320 ,'2 a, 320/6-4, 400/4, 
600/2-6. 

LARGE CAPACITORS 

High ripple current tvpee: 1000,25 5.6; 1000/50 8/2; 
1000/100 18(3; 2000/26 7/4; 2000/50 11,4; 2000/100 28/9; 
2S00/64 16/6; 2500/70 18/6; 500fl,'20 12/6; 5000/50 81/11; 
6000/100 68/3; 10000 .'15 17,'-: 10000/25 24/8: 10000/50 
44/-; 10000/70 61/-. 

MEDIUM RANGE ELECTROLYTICS 

Aiial leads: 30/302/-; 100/25 8,'-; 100/50 2/8; 250/252/6; 
330123 2/8: 250/50 3/B: 500/25 3.9: 500 .'50 4/6: 1000/25 
4/-; 1000/50 8/-; 2000/25 6/-. 

SMALL ELECTROLYTICS 

Axial leads: 4-7/10, 4-7/25, 5/50, 1/- ea. 10/10, 10/25 
10/50, 33/10, 50'10, 1/- ea. 25/26. 25/50, 47/26, 100/10 
220/10, 1/3 ea. 



PEAK SOUND PRODUCTS 
ENGLEFJELD AMPLIFIER 




Build it 
12+18 



23 + 25 



Stereo ampllMr in modular kit iorm ^Including cabinet} 
12 watts per channel £38.6.0; 25 watts 118.15.0. Cabinet 
kit only 68. These prices uett- As recently reviewed 
in Hi Fi Sound. 



BAXANDALL 
SPEAKER SYSTEM 

Designed by Peter Baxandall. SiuperU 
reproduction for Its size. Handles 10 waltq 
with case. Tees EL AC ISO 69RM109 
speaker unit. Kit. 118.12.0 nett.; built] 
(19.8.8 nctt. 






STEREO AMPLIFIER SA.I0-I0 

Developed Irom the very 
successful HA. 8-8 amplifier 
giving first class stereo 
amplification featuring 

separate volume controls lor 
each channel, bass and treble 
controls, mi n;ini per channel into 5 to SQ< Kit 
116. 7.6 nett.; built «84.16.8 nctt. Suitable n(] v, id.; 
range speakers available 113.15.0 each nett. 




MAINLINE AMPLIFIER KITS 

BCA/SG8 designed main ompliflcr kite. Input sensitivity 
S 00 -700m V If.r full output Into 8 n . 

Kit price Suitable unreg. 

Power inclodiQR components power inpjly kit 

12W 168/- nett 98/- 

25W IMS- nett X/A 

40W 310/- nctt 115/1 

70 W 258/- nett 138/10 



30 WATT BAILEY AMPLIFIER KIT 

Special summer reduction (to Sept. 30th, 1970, only). 
Sensitivity 12V for full output into 8(1. Transistors 
for one channel 47.5.6 list, 16 only uett. Transistors lor 
two channels £14.11.0 list 111 only nett. Capacitors and 
resistors (metal oiide) 30/- per channel nett. Complete 
unregulated power supply kit 87/6 nett. 



ZENER DIODES 

5% fuE range E24 values: 400niW: 2-7V to 30V 4,6 ea. 
IW: 6-8 V to 82V 9/- ea. I-6W: 4-7V to 75V 12/- ea. 
Clip to increase 1-5W rating to 3 waits (type 266F) 84. 



CARBON TRACK POTENTIOMETERS, | on g spindle*. 
Double wiper ensures in In I mum noise level. 
S i ogle gan g I lue.'ir 220 Q to 2 -2M 2/8 

.Single gang log 4-7KOto2-2MQ 2/8 

Dual gang 11 tie ii i 4-7KQ to 2-2MO 8/8 

Dual gang ioc 4-7KQ to 2-2MB 8/6 

Logf'aatilog I0K, 47K, lMfl only 8/6 

Dal iiutiini; 10K only B/6 

Any typo with JA D.F. mains switch, extra 2,6. 
Please note: only decades of 10, 22 and 47 are available 
within ranges quoted. 



CARBON SKELETON P RE-SETS 

Small high quality, type PR, linear only 100 O. 220 Q, 
470Q, IK, 2K2. 4K7, 10K.SSK, 47K. 100K.220K, 470K, 
1M, 2M2, 5M, lOMfi, Vertical or horizontal mounting 
1/- each. 



THE NEWELECTROVALUE CATALOGUE 

48 pages— thousands of Items — packed with information — 
8,'- post irce. Add 4/- ii sent overseas by air mail 



COMPONENT DISCOUNTS 

10% on orders for components £or £6 or more. 16% on 
orders tor components for CIS or more (No discount on 
nctt items). 

POSTAGE AND PACKING 

Free on orders oyer tS. Please add 1/6 if under. Over- 
seas orders welcome: carriage charged at cost. 



ELECTROVALUE 



Dept. PE10, 28 ST. JUDES ROAD, ENGLEFIELD GREEN, EGHAM, SURREY 

I Hours: 9—5.30; Sat. 1 p.m. Tel.: Eg ham 5533 (STD 0784-3). Telex 264475 



834 



Practical Electronics October 1970 



Send an S.A.E, lee Few Oompreh entire I.C. and Semiconductor prfve liiti 

INTEGRATED CIRCUITS 

NEW LOW PRICES • FULLY GUARANTEED 



RCA 
CA38Q0 

3005 



•2« 
-.*8B 



39 8 
B3'B 
S7,'« 
14)9 
17/9 
81/- 

t*>i 

18 9 
»'- 
1M 
25 3 
«,'- 
M/- 
267- 
25,9 
»/- 
149 
81/- 
17/8 
38 6 
27/8 
£4/8 
14/8 
189 
82/- 
22/- 
27/8 
24/- 
26;- 
1S7- 
27/8 
42/8 
82/- 
87/- 
27/- 
33,- 
10/- 
22/- 
48/- 
»/- 
267- 



MOTOROLA 

MC724P 

MC788P 

MC789I* 

MC790P 

MC7921' 

MC7991' 

MC1303P 

MC13041' 

MC7DSP 

MC74901 1 

MC7S8P 

MC8S81* 

vx:i:,:\->- 

MCI436P 

MC170DCL 
FAIKCHILD 



Ml 
178 
19/8 
17,8 

27/S 
17/8 
17/9 
67/8 

79/8 
£8/8 
88/6 

19 e 

130/ 
89,8 
86,'- 

18/- 



10 + 
18/- 
178 

15- 
24S 

16/ 
IS; 



l- 
88 
8/6 

12! 6 

SB'S 

21'- 

21 

21/- 

69/- 



L90O 

L914 

1,923 

LTO'iC 

7.7npc 

L710C 

L711C 

L716C 

TEXAS TTL 

BK7400N 

SS7401X 

SN7402N 
SN7403N 
SN7404N 
SN7406S 
SX7410X 
SN7413X 
3N74-20N 
SN7430N 
SN7440X 



ll-ll 
87- 
8/- 
11/9 
32 B 
19 8 
186 
19 6 
60/- 



]■!+ 
7/8 
7/8 

11/- 
£8/6 

tu- 
rn 

Ith 



aa+ 

188 
1$/- 

13 8 

281- 
18/6 
18/6 



116/- [ 

79 8 

59 8 | 



6/9 
69 



MDLLARD 

LIKEAR 

TAA241 

24'J 

■J43 

968 

KM 

300 
310 
320 
860 
•SB 
S21 

tsa 

530 

811 
TAB 101 
TAD1O0 
TAD] 10 



32 6 

85 

30 - 

16/8 

18/6 

3S/- 

26,'- 

14/8 

36/- 

29/6 

£6/6 

78/- 

»/- 

8t/- 

19/6 

39 6 

39 6 



MTJLLARD DTL 



17/- 

17/- 

17/- 



.8 ■ 

8 

8 - 
S 3 

e 3 

e 

22 



FJH12) 
PJHX41 

KJJI161 
KJH17! 
KJH221 
FJJ1Q1 
l'JJ121 
l'JJ141 
KFJ191 
PJJ231 
FJY101 
per type i 



17/8 
17/6 

17.6 
17/6 
18/8 
17/6 
27/8 
37/6 
62/8 
37/8 
82/8 
18- 
pt L90O' 



Data Sheets all 1 

914/923 and PIcsaev'2'6 

8 Pin To -5 I.C. Holders, 10/6 

U Pin Dual-ln-Linc I.C. Holder*. 11- 

16 Pin Duul-tn-Linc r.C, Hol.kis, 18 8 



FCH1P1 
FCH121 
PCH2U1 
PCH23 1 
FCJI01 
FCJ111 
FCJ201 
FCJ211 
FCK10I 
FCYI01 

PLESSEV 
HL402A 
91-403 A 
SL701C 
SL702O 

GENERAL 
ELECTRIC 

FA222 
FA230 
PA234 
P-A237 
PA24« 
PA4'24 



17/6 

21/ 

28/6 

30/- 

38/8 

31/- 

38/ 

66 

87/6 

21 - 

48/8 
42/6 
89/6 

29 6 



87.6 
22/8 
21/8 
SS/- 
62/8 
46/- 



FMt & Packing 1,6 per order. Data sheet tree if ordered with ICS. Send 2/6 (or catalogue 

TE ^rn?M E A. MARSHALL & SONS LTD. ™* 

28 CRICKLEWOOD BROADWAY, LONDON. N.W.I 

CALLERS WELCOME 9-5.30 SATURDAY 9-5 

SEE OUR MAIN ADVERTISEMENT ON PAGE SOS FOR SEMICONDUCTORS 



BUILD YOUR CIRCUITS 
on 

VEROBOARD 

—the Universal Wiring Board—' 

obtainable from your local Retail 

Trade enquiries to : 

NORMAN ROSE (ELECTRICAL) LTD. 

8 St. Chad's Place, Gray's inn Road, London, W.C.I 

Technical enquiries lo : 

VERO ELECTRONICS LTD. 

Industrial Estate, Chandler's Ford, Hants 




... now the "GR.84", build it in only 20 hours 

using our factory- made, fully tested units 

ir Includes 'String Bass' and 

' Growl ' features 
^ Internal 10 watt amplifier and 

loudspeaker 
•J? Uses latest integrated circuits 
■]!(■ 49-notes, 8 stops, glide, 

vibrato, etc, 
-jfc- All units available separately 

Price £1 12.10.0 complete 

(terms available) 

Other kits from £81.10.0 

Harmonics 

(Bromley) Ltd. *^r 

PE2, Clarion Works, Napier Road, Bromley, Kent 01-4602122 




Ifyoucanput 
a 'Yes' in every box, 
you might 
just make a 

RADIO TECHNICIAN 

in Air Traffic Control 



An all-consuming interestin 
telecommunications 

At least one year's practical experience 
in telecommunications, preferably with 
'ONC or 'C and G' technical 
qualifications 

A highly developed sense of 
responsibility 

Willingness to undergo a rigorous 
programme of training 

Aged 19 or over 



□ 
□ 
□ 



To the right man, the National Air Traffic 
Control Service offers the prospect of an 
interesting and steadily developing career as 
a Radio Technician in air traffic control. 

The work involves the installation and maintenance 
of some of the very latest electronic equipment at civil 
airports, radar stations and other specialist 
establishments all over the country. Important today, 
the job will become increasingly vital as Britain's air 
traffic continues to grow, and prospects for promotion 
are excellent. Starting salary varies from £1 044 (at 1 9) 
to £1373 (at 25 or over). Scale maximum £1590 
(higher rates at Heathrow). The annual leave 
allowance is good, and there is a non-contributory 
pension for established staff. 

If you feel you can meet the demands of this rather 
special job — and you have a strong determination to 
succeed — you are invited to complete the coupon 
below. 



Send this coupon for full details and application form 
To I A J Edwards, C Eng, M IEE, The Adelphi, 
Room 705. John Adam Street, London WC2, 

marking your envelope "Recruitment". 



Address 



I 

Ii -* \j i oMjjHvourc iu icaiuciiia uuiiiue 
. IU ATCS 

| N. 



JPET/G2 
No! applicable to residents outside the United Kingdom 



National Air Traffic Control Service 



I 

I 
I 



Practical Electronics October 1970 



835 



Practical Electroaics Classified Advertisements 

RATES: 1/6 per word {minimum 12 words). Box No. 1/6 extra. Advertisements must be prepaid and addressed to Classified 
Advertisement Manager, "Practical Electronics" IPC MAGAZINES LTD., Fleetway House, Farrmgdon Street, London, E.C.4 



-TOP TRANSISTORS— 

ACY22 1/9 OC45 1/9 ZTX300 1/9 

BCI68 1/9 OC7I 1/9 2N706 1/9 

BCI69 1/9 OC72 1/9 2N2926 1/9 

BSY27 1/9 OC200 1/9 2N3705 1/9 

BFYSI 1/9 OC20I 1/9 2N3706 1/9 

BFYS2 1/9 OC202 1/9 2N3708 1/9 

All che above types are available at 16 for £1. 
Brand New. Individually Tested, unmarked, 
but guaranteed to be within their correct 
specification, or money refunded. 

ANTEX SOLDER IRON 

A lightweight iron with a 15 watt nickel 
plated bit. Designed to enable you to weld 
reliable joints accurately. Model CN240 volts. 
Special low price. Act Now, Only 29/1 1 . 
MONEY BACK GUARANTEE. P. & P.i/- 

J. M. KING (O) 
17 Buckridge, Portpool Lane, London, E.C.I 



MUSICAL MIRACLES! Drum, Cymbals, Waa- 
waa and Fuzz modules. New unique effects 
unf U, Percussion, et c. Good waa-waa kits *B/-. 
Famous "Mister Bassman" bass pedal unit. 
Also bargain components list of reed switches, 
etc. Send S.A.E. NOW! D.E.W. LTD., 254 
Rtngwood Road, Ferndown, Dorset. 



ENAMELLED COPPER WIRE 
S.W.G. Per *lb reel Per lib reel 

18-22 11/3 16/« 

23-30 11/9 17/6 

31-35 U/3 18/6 

36-40 15/- 24/- 

41-44 17/9 29/6 

Orders despatched by return of post. Please 
add 1/- per item P. & P. Supplied by : BANNER 
TRANSFO RMERS, 84 Old lansdowne Road, 
West Didsbury, Manchester, 20. TRADE 
ENQUIRIES INVITED. 



ALL THOSE LITTLE ITEMS which you can 
never And are available from our stock. Also 
speaker fabrics, BAF wadding, Peerless 
speakers, cabinet kits, cross-over's. For full 
details send 9d. in stamps to: AUDIQSCAN, 
Dept. PE, 4 Princes Square, Harrogate, 
Yorks. 



NO NEED TO WORRY ABOUT 
A TRANSMITTING LICENCE 

because this GPO approved transmitter/ receiver 
kit does not use R.F. and you can get one easily. 
Your transmissions will be virtually SECRET since 
they won't be heard by conventional meant. 
Actually it's TWO KITS IN ONE because you get all 
the printed-circuit boards and components for both 
the transmitter AND receiver. You're going to find 
this project REALLY FUIM-TO-BUILD with the 
EASY-TO-FOLLOW instructions. An extremely 
flexible design with quite an AMAZING RANGE — 
has obvious applications for HOUSE-TO-HOUSE 
USE, SCHOOL PROJECTS, LANGUAGE 
LABORATORIES. SCOUT CAMPS, etc. 

GET YOURS ! SEND 95/- NOW 

TO; 'BOFFIN KITS* 

4CUNLIFFE ROAD 
STONELEIGH, EWELL, SURREY 



CLEARING LABORATORY, scopes, V.T.V.Ma, 

V.O.M's, H.S. recorders, transcription | 
turntables, electronic test meters, calibration 
units, P.S.U.'s, pulse generators, D.C. null- 
potentiometers, bridges, spectrum analysers, 
voltage regulators,- sig-gens, M/C relays, 
components j etc. Lower Beetling 236. 



MISCELLANEOUS 



BIG BARGAIN PARCEL 13/- 

POST PAID 
Containing multi-contact relay, transistors, 
resistors (some high scab), rectifiers, diodes, 
capacitors, pots, knobs, etc. 

"SHURE" TAPE HEADS 

Record/playback and erase in one unit, mounted 
on bracketwith tape guide, etc. tOj- pose paid. 
"MARRIOT" single record, playback heads. 
5/* post paid. 

PHOTO ELECTRIC SWITCH KIT 

Light cell transistor, relay, etc. Elegant case in 
hammer blue 5J"x l*" *4±" fltted wi,n ''« nt 
hood, ideal counter alarm, dawn/dutk switch, 
etc. 35/- poit paid. 

6 OR 12 VOLT 
FLUORESCENT LIGHTS 

12 ins, 8 Watt tube ample light Tor caravan, 
tent, etc. Fully transistorised, low battery drain. 
Unbeatable at RK/fi 

■w/ u post paid, 
or in kitform 57/6 



4 WATT GRAM AMPS. 

Volume and tone controls, mains operation, 
3Q output, new and boxed "7? If% POST 
**/ PAID 
SALOP ELECTRONICS Callers welcome 
3J Wylti Cop „ - - - ... 

Shrewsbury. Shropshire S.A.E. for ln» 



CASES. Perfect West Hyde. 9in x 5tn x 61n, 
fitted handle, feet, cable hole. Without panel, 
screws supplied. 36/- each, C.W.O. 
C, PURVES, 145 North Station Road, 
Colchester. 



LIVE WIRES can be dangerous. Now you can 
make electrical connections safely in seconds 
with the revolutionary new Keynector. Cuts 
out plugs, sockets and bare wire dangers. 
Ideal for bench and high speed testing of 
electrical equipment ... a must for the do-it- 
vourself fan. Send for a Leaflet to E. B. 
INSTRUMENTS (Dept. PE), 49/53 Pancras 
Road, London, N.W.l (01-837 7781). Only 
46/6 plus postage. 



AMAZING VALUE 

NEW BRANDED FULL SPECIFICATION 

DEVICES 

Integrated Circuit* Complete with Data: 
N57Q9A Type 709 Op. Amp., U/« 
GE PA234 IW Audio Amplifier, 17/tV 
GE PA237 2 W Audio Amplifier, 31/6 
Plessey 5L402A Preamp, and 2W Amp. (en ui v. 

IC 10) with instructions, 40/- 
GE D40tl 4W Darlington Amplifier Very 

High Gain 10,000 min., 13/6 
MEL 1 1 Photo Darlington Amp., 9/6 
Connectors for D.I.L, I.C.s, •/- 

High Quality Low Coat Traniistore: 
CfE2N5172, 1/9 MUL BFX86. 6/- 

MEQ4I2 3/9 MUL BD 1 24, 12/- 

T! 2N40S9, 3/6 S 2N30S5. 14/- 

Triaci for Full Wave Powar Control: 
RCA 40669 BA 400V. 14/- 
RCA 40583 Trigger Diode, 5/3 

Plastic Rectifiers for Power Suppliae: 
ITT I Amp. 4000 series . 

llsMOOl, 50V, 1/9 IN40O4. 400V, 2/5 

IIM4002. 100V, It- IN4005, 600V, 1/9 

1 N4003, 200V, 2/2 I N4O06. BO0V, 3/5 

1 N4O07, I OOOV, 4/- 
W0OS I A 50V full wave bridge Si, 7/6 
PD40 2A 400V full wave bridge Si, 12/6 

JEF ELECTRONICS (P.E.IO) 
York House, 12 York Drive, G rap pen hall 
Warrington, Lanes. Mail Order Only 

C.W.O. P. & P. I/- per order. Overseas 7/6. 
Money back if not satisfied. 



MORE ROBOTS 

Synthetic Animals with "BRAINS" of their 
own. The LATEST range of project! 
include; an electronic 'animal' which 
"LEARNS", and an Electro Chemical device 
capable of "REPRODUCING" itself! 
Other projects SURE TO INTRIGUE YOU 
are a transmitter/receiver which radiates 
without using r.f. so there's NO NEED TO 
WORRY ABOUT A LICENCE, also TEN 
new projects, one of which is an electronic 
dice machine. HOSTS OF EASY-TO- 
CONSTRUCT projects, for anyone with a 
basic knowledge of Electronics, DONT 
WAIT. SEND 3/- for your list— NOW! 

To: -BOFFIN PROJECTS' 

4 CUNLIFFE ROAD 

STONELEIGH. EWELL, SURREY 

Designed by GERRY BROWN and 

JOHN SALMON and presented 

on T.V. 



VICTORIA STREET'8 unique magazine and 
paperback centre.. Hills Westminster. Practwal 
Wireleiw always in stock. HILLS V EST- 
MINSTER LTD.. 5 Artillery How, Victoria 
Street, S.W.I (01-222 6165). 



PHQT0TRAN8I8TORB. Similar OCP71, only 
7/6 each or two for 12/-, P.B. ELECTRONICS, 
3 Fernslde, Amberlands, Backwell, Somerset. 



BUILD IT in a DEWBOX quality cabinet 
2in x 21in x any length. DEW LTD., 
Ringwood Road, Ferndown, Dorset. S.A.E. 
for leaflet. Writ* now— right now. 



PARAPH YSICAL LABORATORY, Downton, 
Wilts, Telekinetic phcitographs/data. S.A.E. 
for list . Samples 20s. 



SERVICE SHEETS 



LARGE SUPPLIER 
OF 

SERVICE SHEETS 

T.V., RADIO, TRANSISTORS, TAPES, GAR RADIOS 

5/- EACH, MANUALS FROM 10/- 
PLUS LARGE S.A.E. 

(Uncrossed P.O.'s please, original 
returned II service sheets not available.) 

FREE TV FAULT TRACING CHART OR TV 
LIST ON REQUEST WITH ORDER 

C. CARANNA 

71 BEAUFORT PARK, LONDON, N.W.I I 

MAIL ORDER ONLY 



SERVICE SHEETS. Radio, TV, etc., 8,000 
models. List 2/-. S.A.E. enquiries, TELRAY, 
ll.Maurtland Bank, Preston. 



SERVICE SHEETS (1 925-1970) for Tele visions, 
Radios, Transistors, Tape- Recorders, Record 
Players, etc., by return post, with free Fault- 
Finding Guide. Prices from 1/-. Over 8,000 
models available. Catalogue 2/6. Please send 
S.A.E. with all orders/enquiries. HAMILTON 
RADIO, 54 London Road, Bexhill, Sussex. 



RADIO TELEVISION, over 8,000 Models. 
JOHN GILBERT TELEVISION, lb Shep- 
herds Bush Rd., London, W.6. SHE 8441, 



836 



Practical Electronics October 1970 






WANTED 



CASH PAID for New Valves, Payment by 
return. WILLOW VALE ELECTRONICS. 
4 The Broad wav. Harwell. London. W.7. 
01-567 5400,2971. 



HI-FI EQUIPMENT 



8HUREGOLDRING Cartridges. Post Free. C800, 
M44/5/7 £7.17.6. }i:}J> £5.5.0. 1144 E £8.19.6. 
M55E £9.19.6. M76E/2 £16.10.0. Garrard 
SP25/2 £10.17.6. A P.75 £16.17,6. P. & P. 7/0, 
ULTIMATE ELECTRONICS, 38 Achilles 
Road, London, X.W.fl. Mail Order Only. 



BOOKS AND PUBLICATIONS 



SURPLUS HANDBOOKS 

19 set Circuit and Notes 7 - P.P. 9d 

1155 set Circuit and Notes .... 7/- P.P. 9d 
H.R.O. Technical Instructions . . t!~ P.P. 9d 

38 set Technical Instructions 6/- p.p. id 

4fi set Working Instructions. . , , </- P.P. 9d 
88 set Technical Instructions. .. , 7'6 P.P. 9d 

BC. 221 Circuit and Notes «/- P.P. 9d 

Wavemcter Class D Tech, Instr 67- P.P. 9d 

IB set Circuit and Notes 6/- P.P. 9d 

BC, 1 000 (31 set) Circuit 8. Notes 6'- P.P. 9d 
CR, 100,6.28 Circuit and Notes 10/6 P.P. I .'- 

R.I 07 Circuit and Notes 7/6 p.p. 9d 

A.R.88D. Instruction Manual, .. . 18/6 P.P. 9d 

62 set Circuit and Notes 7/- P.P. 9d 

52 set Sender & Receiver Circuits 8'- post Free 
Circuit Diagrams 5/6 each post free 
R.III6/A, RJ224 A. R.I 355, R.F. 24, 2S, & 26 
A. II 34, T.I 154. CR.300. BC.342, BC.3I2 
BC348.J.E.M.P. BC.624. 22, 1475(88), (392, 
Colour Code Indicator 2/6 P.P. 6d, 
S.A.E. with all enquiries please 
Postage rates apply to U.K. only. ■ 
Mail order only to : 

Instructional Handbook Supplies 

Dept. P.E,, Talbot House, 28 Talboc Gardens 
Leeds 8 



SPECIAL OFFER 

THE FIRST VOLUME ON TRANSISTORS 

in a new series entitled 

THE 

SEM/CON INDEX 

to be published in conjunction with 

AVO LIMITED 
will be ready at the end of September 

Designed to provide comprehensive tech- 
nical data on semiconductors and to be 
updated annually, the first volume covers 
over 16,000 transistors of international 
origin with IS sections, a cross reference 
index, over 600 outline drawings, CV 
numbers, equivalents and manufacturers. 

Invaluable to all Engineers & Buyers 
SECURE YOUR COPY NOW 

Send the special pre-publication offer price 

of 79 /6d + 5/6d p & p, direct to 
Functional Publication Services Ltd, 

29, Denmark St., Wokingham, Berks.. 
(Normal price to be 95/-) 



SITUATIONS VACANT 



A.M.I.E.H.E., A.M.S.E. (Elec), City & 
Guilds, G.C.E., etc., on "Satisfaction or Refund 
of Fee" terms. Wide range of Home Study 
Courses in Electronics, Computers, Radio, 
T..V., etc. 132-page Guide— FREE. Please 
state subject of interest. U1UTISH 
INSTITUTE OF ENGINEERING TECH- 
NOLOGY (Dept. 124 K), AJdermaaton Court, 
Alderniastou Berks. 



ELECTRONICS TECHNICIANS 

living in the 
SOUTH YORKSHIRE AREA 

SOUTH YORKSHIRE AUTOMATIC 
CONTROL ENGINEERING LIMITED 

require technicians age 2 1, .'30 having experi- 
ence in field of design and/or manufacture 
of Control Systems and electronic instru- 
ments. 

Qualifications whilst of interest are not as 
necessary as a genuine desire to work hard 
and grow with afirm already well established. 
Salary range: £700 — £1,500 per annum. 
Apply to: 

The Managing Director 

SYACE Limited, Abbeyfield House 

Blyth Road, Maltby 

Rotherham, Yorkshire 



EDUCATIONAL 



GET INTO ELECTRONICS — big opportunities 
for trained men. Learn the practical way with 
low-cost Postal Training, complete with 'equip- 
ment. A.M.I.B.R.E., E..T.E.B., City .Sf Guilds, 
Radio, T/V, Telecoms., etc. For FREE 100- 
page book, write Dept. 856K, CHAMBERS 
COLLEGE, College House, 29-31 Wrights 
Lane, Kensington, London, W.8. 

ENGINEERS. A technical certificate or 
qualification will bring you security and much 
better pay, Elem. and adv. private postal 
courses for C.Eng., A.M.I.E.R.E., A.M.S.E. 
{Mech. A Elec.), City <fc Guilds, A.M.T.M.I., 
A.I.O.B. and G.C.E. exams. Diploma courses 
in all hranches of Engineering — Mech., Klec, 
Auto, Electronics, Radio, Computers, 
Draughts., Building, etc. For full details write 
for FREE 1 32- page guide.. BRITISH 
INSTITUTE OF ENGINEERING TECH- 
NOLOGY (Dept. 125K), Aldermaston Court, 
Aldermaston, Berks. 



BOURNEMOUTH COLLEGE 
OF TECHNOLOGY 



A CAREER FOR 
MEN OR WOMEN IN 
ELECTRICAL OR 
ELECTRONIC 
ENGINEERING 

UNIVERSITY OF LONDON 
EXTERNAL DEGREE IN 
ELECTRICAL ENGINEERING 

B.Sc. (Eng.) with Electronics 
3 years full time 

Entry requirements: 
Maths (Pure & Applied) \, A , . . 
Physics / A level 

+ Chemistry 'O* level 

Study by the sea in Britain's foremost 
ail-seasons' resort. 

Enquiries for prospectus and further 
information to: 

The Principal, Room 87 
College of Technology 
Lansdowne 
Bournemouth BHI 3JJ 




Established 1891 



. TECHNICAL TRAINING 

llUtf IN RADIO, TELEVISION AND 
ELECTRONIC ENGINEERING 

First-class opportunities in Radio and Electronics await the i C S trained man. 

Let I C S train YOU for a well-paid post in this expanding field. 

ICS courses offer the keen, ambitious man the opportunity to acquire, quickly and 

easily, the specialized training so essential to success. Diploma courses in Radio/ 

TV Engineering and Servicing, also Colour TV Servicing, Electronics, Computers, 

etc. 

Expert coaching for: 

* C. a> G. TELECOMMUNICATION TECHNICIANS' CERTS. 

* C. & C. ELECTRONIC SERVICING. 

« R.T.E.B. RADIO AND TV SERVICING CERTIFICATE. 

* RADIO AMATEURS* EXAMINATION. 

* P.M.G. CERTIFICATES IN RADIOTELEGRAPHY. 
Examination Students coached until successful, 

NEW SELF-BUILD RADIO AND ELECTRONIC COURSES 

Build your own 5-valve receiver, transistor portable, signal generator and 

multi-meter. All under expert guidance. 

POST THIS COUPON TODAY and find out how I C S can help YOU in your 

career. Full details of I C S courses in Radio, Television and Electronics will be 

sent to you by return mail. 

MEMBER OF THE ASSOCIATION OF BRITISH CORRESPONDENCE COLLEGES 



INTERNATIONAL 

CORRESPONDENCE 

SCHOOLS 



A WHOLE WORLD 

OF KNOWLEDGE 

AWAITS YOU! 



r 

! 
I 



International Correspondence Schools 

(Dept. 152), Intertext House, Stewarts Road, | 

London. S.W.8 



NAME „ 

Block Capitals Please 

ADDRESS 

! :::::: ! 

— - 10.70 ■ 



Practical Electronics October 1970 



837 



RECEIVERS AND COMPONENTS 



POLYSTYRENE CAPAC1TOR8: 125/350V 150, 
ISO, 330, 390, 560, 680, 820, 1,800, 2,200, 
2 700, 5.600, 6.800, 8,200; 125V 18, 22, 120, 
220, 1,200, 1,500, 3,300, 3,900, 0.01. 0.012. 
O.015. Paper: 100V Q.0001, 0.001, 0.002, 0.005, 
3/- doz. Computer Panels: 5-BC108, Diodes, 
3/-, 4-10/-; 8-OC76, 8-0 A10, 7/6; 4-OC42, 3/-; 
8-OC43/OKT875, 24-OA81, T/6; 24-A1678, 
550 MEG pnp. 24 Diodes 10/-; 3-OC23, 8 
Diodes 10/-, Mixed Transistors on Panels 
100 20/-. Brand New Chassis: 2-OC35, 2-OC29, 
12-W.W Resistors, 257-. Electrolytic*: 4,000, 
60V, T/6. Post 1/6 order. J.W.B. RADIO, 
75, HavSeld Road. Sal ford, 6, Lanes. 



A CORNUCOPIA OF COMPONENTS! Scarce 
valves, selected TV components, speakers and 
cabinets. Computer panels — long leads, NOT 
printed circuits. Transistors, resistors — newand 
recovered. State vour requirements. S.A.E. 
for details MAIL- MART, 6 Eastbourne Road, 
Pevensey Bay, Sussex. 



RECEIVERS AND COMPONENTS 

(continued) 



NEW It. 2 

Psychodelic Lighting Unit 




This new psychodelic lighting unit 
offers even greater sensitivity than ou,r 
original unit, requiring typically only 
1V r.m.s. for full drive. It features 
higher input impedance circuitry for 
less loading of speaker lines and is now 
manufactured on professional fibre- 
glass printed-circuit board material. 

Drive voltage is derived directly from 
amplifier output or across speakers, 
The unit converts the audio frequency 
signals into a three-coloured light dis- 
play; the colour depending on the 
frequency of the signal and the Inten- 
sity on the loudness of the audio 
source. 

Uses latest full-wave triac circuitry 
and incorporates signal input level and 
minimum ambient light level controls. 
Will drive up to 1'5kW per channel at 
240V a.c. Complete printed-circuit 
board assembly built and tested. Size 
8}in 6iln < 3*in. 

£17.10.0 net plus 10/- carriage 

MAIL ORDER ONLY 

Dabar Electronic Products 

98a Lichfield Street, Walsall, Staffs. 



GUARANTEED TUBES AT 
REDUCED PRICES 



We are the area stockists for Display Elccironics 
Re-manufauured Tubes. These tubes have a 
complete new gun assembly, the glass Is the only 
reconditioned part and that cannot wear out. 
We Invite enquiries from the trade or the public, 
Daibi 9.30-5,30. Frt. 0.30' 8, » tloted Mondait. 

TELEVISION CITY 
SO Richmond Road. Kingston, Surrey 
Telephone 01-546 3961 (100 yards from station I 



FULL SPECIFICATION COMPONENTS 

Electro ly ties SO uf at 50 volt* 2/- each . 
Plessey SL403A I.C amplifiers 45/- each. 
Plessey SL702C op, amplifier! 21 i- each. 
2N17I I silicon planar transistors 5/6 each. 
2N706 3/-; 2NI305 3/3; SCI 06 2/3; 
2/- p. SI p. on orders under £2. Catalogue I/-. 

SPECIALIST ELECTRONICS CO. 

2& York Road, Crosby, Liverpool L23 5TS 



DIODES suitable for line sync circuits in 
T/Vs, switching circuits. Organ Builders— 
untested, unmarlsed. £S per 1,000 plus 1/- 
P. & P. C.W O. to MRS. M. EVANS, 3a High 
Street, Teddington, MMdx. 



TOP PRICES PAID 

for new valves and component! 

Write: 

KENSINGTON SUPPLIES 

(B) 367 Kensington Street 
Bradford 8, Yorks. 



R & R RADIO 

51 Burnley Road, Rawtenstall 

Rossendale, Lanes 
Tel.: Rossendale 3152 

VALVES BOXED, TESTED * GUARANTEED 



E8F80 


il- 


PCC84 


1/- 


PY8I 


1/6 


EBFB9 


ia 


PCF80 


Jh 


PYB2 


J/- 


ECC62 


31- 


PCF82 


3/6 


PY800 


3/6 


ECL60 


v- 


PCLB2 


it" 


PY80I 


3(6 


EFB0 


1/6 


PCLB3 


4/- 


UI91 


4/6 


EFSS 


V- 


PL36 


31- 


30FS 


2/6 


EY84 


41- 


PL8I 


41- 


30PI2 


4/6 


EZ40 


4/6 


PL83 


4h 


30CIS 


5/- 


EBC4I 


4/6 


PY33 


5/- 


50CD6G 


7/6 


PO 


ST, ON 


E VALVE »d 


.TWO 


TOSIX6d. 






O 


/ERSIX POSTPAII 


X ■ 





BRAND NEW ELECTROLYTICS 15/18V 
0-5, 1, 2, 5, 10, 20, 30, 40, 50, lOOmF, 8Sd. 
El 2 series 5% resistors, Carbon Film iW 
in to lMfl, t-5d. Wirewound 5W 15tl 
to 15KQ, IQd. Postage t/-. Tim C.R. SUPPLY 
CO., 127, C.'hL'sterfleld Rd., Sheffield, S8 OE.X. 



NEW MODEL V.H.F. KIT MK2 

Our latest Kit, improved design anil performance plus 
extra Amplifier Stage, receives Aircraft, Amateurs, 
Mobile, Radio 2, 3, 4, etc. 

This novel little set will give you endless hours of pleasure 

and can be built in one evening. Powered by 9 Volt 

battery, complete with easy to follow instructions and 

built in Jack Socket for use with Earphones or Amplifier. 

Only 68;-. P. ft P. Free U.K. only 

Postal Orders, Cheques to- 

Dept. F.E. 

Galleon Trading Co., 25 Avelon Road, 

Romford, Essex 



RECEIVERS AND COMPONENTS 

(continued) 



15 WATTS FOR £5.5.0!! 

Now available for return of post 
delivery— "Hardcastle" ISW Ampli- 
fier kit as described in Hi-Fi News. 
This outstandingly low price includes 
Fibreglass PCS with screened legend 
for. easy assembly, heatsink, tran- 
sistors, low noise resistors, capaci- 
tors and misc. hardware, circuit 
diagrams and post packing and insur- 
ance, A unique feature is that the 
output power can be varied from 
10 to 30 watts and the output imped- 
ance between 8 and 15 ohms. {Basic 
kit at £5.5.0 gives 15 watts/15 ohms), 
An ideal educational project. Send 
now for your kit by return of post or 
send a stamped self-addressed enve- 
lope for details to: 

L.S.T. ELECTRONIC COMPONENTS LTD. 

DEPT. PE77 
7 C0PTF0L0 ROAO, BRENTWOOD, ESSEX 



PRINTED CIRCUITS. Capacity now available. 
Send artwork for quote, S.A.E. Sample 1 off. 
Artwork, reduction, negative, 4d. per. sq In. 
iin Fibredass. 1/6 per sq in. including turning. 
Drilling extra. FREEMAXTLE, 18 Pennine 
Itniid. Millbrook, Southampton. 



PRINTED CIRCUIT BOARDS for P.E. PROJECTS 

All boards drilled and roller tinned complete 

with layout drawing, 

EXAMPLES . 

Marine Tachometer (May 1970) 5i-ea, Musical 

Stave (May 1970) 67- ea. 

Waa-Waa pedal Vol. 4 No, 7 1/9 ea. Audio Sig. 

Gen. (Sine and Square on one board) Vol. 5 No. 

I0 8i'6ea. 

S A E for Use. Now available from:- HENRY S 

RADIO LTD., Edgware Road, London, YV.2 

P.H. ELECTRONICS, Industrial Estate. 

Sandwich, Kent, Tel. 2517 



OFFER. Copper laminated A* 11 fibreglass. 
Board single-sided 4d. per sq in. Double -sided 
5d. per sq In. Any size cut. Minimum order 10/-. 
P. <fe P. plus 10% • FKEEMAXTLE, 18 Pen- 
nine Road, MiUbrook, Southampton. 



ELECTRICAL 







BEST EVER 200 140 VOLT "MAINS" 
SUPPLY FROM 12 VOLT CAR BATTERY 

Exclusive World Scoop Purchase. The fabulous 
Hk. I2D American Heavy Duty Dynamotor 
Unit with a Massive 220 watt output and 
giving the most Brilliant 200/240 vol t perfor- 
mance of all time. Marvellous for Television, 
Drills, Power Tools, Main* Lighting, AC 
Fluorescent Lighting and all 200/240 volt 
Universal AC/DC mains equipment. Made at 
tremendous cost for U.S.A. Govt, by Delco- 
Remy This magnificent machine is unobtain- 
able elsewhere. Brand New and Fully Tested. 
Only £4.19.6 + 10/6 postage. C.O.D. with 
pleasure, refund guarantee. Please send S.A.E. 
for illustrated details. 
Dept, PE, STANFORD ELECTRONICS 
Rear Derby Road. North Promenade 

Blackpool, Lancashire 



838 



Practical Electronics October 1970 




FOR SALE 



SEEN MY CAT? 5,000 items. Mechanical and 
Electrical Scar, and materials, S.A.E. K. B.. 
WHTSTOX. Dept. PE, New Milis. Stoekport. 



WEST SOUND 

STEREO TEN AMPLIFIER 

150V-marns operation, low hum, featuring 
separate volume and tone controls for each 
channel. BYIOC, ECC83. 2 EL84. Size 
8 6 Si in. Output 5 + 5 watts into 30. 
Input 300 m v for full output, 9 gns built 
and tested, kit 7 gns chq P.O. to West 
Sound, 30 Brompton Ave,, Scfton Park, 
Liverpool 17, 



COMPREHENSIVE STOCK of relays, counters, 
timers, switches, etc. Low prices, immediate 
despatch. 01-44O-1293 after 11 p.m. 



NEW CATALOGUE Xo. Id, containing credit 
vouchers value 10/-, now available. Manu- 
facturers' new and "surplus electronic and 
mechanical components, price 4/8, post free. 
ARTHUR SALLIS RADIO CONTROL LTD., 
28 Gardner Street, Brighton, Sussex. 



MORSE 



MADE 
EASY 



I I 



FACT NOT FICTION. If yon start RIGHT 
you will be reading amateur and commercial Morse 
within a month Inormal progress to be expected). 

Using scientifically prepared 3 -speed records you 
automatically :earn to recognise too code RHYTHM 
without translating. You can't help It, it's as eaHV as 
learning a tune. 1 S tV.P.M. in 4 weeks guaranteed. 

For details and coarse C.O.D. ring S.T.B. 01-G60 2898 
or send 3d, stamp for explanatory booklet to: 
Q3HSC (Boi It)), 45 GREEN LANE, PHRLEY SURREY 



PLEASE MENTION 
PRACTICAL ELECTRONICS 

When Replying to 
Advertisements 



BATTERY ELIMINATORS 

The ideal way of running your TRANSISTOR 
RADIO, RECORD PLAYER, TAPE RECORDER, 
AMPLIFIER, etc. Types available : 6v, 9v, I2v, 
I8v (single output) 39,6 each. P. & P, 3/9. 
9v + 9v; Gv -f 6v; or 4Jv + 4|v (two separate 
outputs) 42.fi each. P. & P. 3/9. Please state 
output required. All the above units are 
completely isolated from mains by double 
wound transformer ensuring I00".i safety. 

R.C.S. PRODUCTS (RADIO) LTD. 
(Dept. P.E.), 31 Oliver Road, London, E.I7 



AERIALS NEW CONDITION 

Whip Type lift. 12/6 each. 

Used condition 12ft. 10/- each. 

All collapsible Type. Post and 
packing 3/6. 

Bases for the above 5/-, Post and 
packing 2/6. 

C.W.O. Carriage Charges Main- 
land Only. 

A. H. Thacker, Radio Dept. 

High Street, Cheslyn Hay 

Near Walsall, Staffs. 



NEW RANGE U.H.F. TV AERIALS 

All U.H.F, aerials now fitted with lilting bracket 
and 4 clement grid reflectors. 

Loft Mounting Arrays, 7 element, 40.-: 
U element, 47 6; 1+ element, 55 -; IS element, 
B2 8. Wall Mounting with Cranked Arm, 
7 element, 60 -; 11 element, 67,0; 14 element, 
75 -; 18 element, 82 6. Mast Mounting with 
2tn. clamp. 7 element, 42 8: II element, 55-; 
14 element, 62-; IS element, 70-. Chimney 
Mounting Arrays, Complete. 7 element, 
72 6; 11 element, SO -; 14 element, 87 6; IS element, 
95 -. Complete assembly Instructions with every 
unit. Low Loss Cable, I 8 yd. L'.H.F. Pie- 
amps from 75,-. State clearly channel number 
required an all orders, 

BBC ■ ITV AERIALS 

BIJC (Band I). Loft, 35-. 
External S D, 30 -. "H", 
£3.15.0. 

ITV (Hand 3). 3 element toft 
array, 30 -. 5 element, 40 -. 
7 element, 50 -. Wall mounting, 
3 element, 50. -. 5 element, 55 -, 
Combined BBC ITV. Loft 
i + 3, 40/-: i - 5, so;-: i - ?, 
CO,'-; Wall mounting 14-3, 
60.-; 1 + 5, 70 -: Chimney 
1 + 3,70-; 1 + 5,80-. 
VTIF transistor pre-amps, 



COMBINED BBC1— ITV— BIK'2 AERIALS 

I + 3 + ?,70 -. 1 + 5 + 9, 80 -. 1 + 5 + 14,90 -, 
I + 7 + 14, 109 -. Loft mounting only. 

F.M. (Band 2). Loft S D, 17 6, T, 35 -, 3 

element, 57 6. External units available. Co-ax. 
cable, 8d. yd. Co-ax. plugs, ] e. Outlet boxes, 5 -. 
Dlplexer Crossover Boxes, 17 S. C.W.O. or C.O.D. 
P. & P. 6/6. Send 6d. stamps for illustrated lists, 

CMLERS WELCOME 

OPEN ALL DAY SATURDAY 

K.V.A. ELECTRONICS (Dept. p.e.) 

40-41 Monarch Parade 

London Road, Mitcham, Surrey 

01-648 48S4 




CLASSIFIED 



Your classified advertisement will 
be seen by more than 480,000 
readers of 

PRACTICAL 

ELECTRONICS 



For details of how to send your 
instructions please see page 836. 



ADVERTISEMENTS 



MAKES 5 DIFFERENT 



TRANSISTOR RADIOS 
TOTAL BUILDING PRICE 



Last 250 

39 6 



Amazing Radio Construction 
set 1 Become a radio expert for 
39/6. A comptet e Home Radio 
Course. No experience needed. 
Parts including instructions for 
each design. Step-by-step plan, 
all Transistors, loud* 
apeaker.^personal phone, 
knobs, screws, etc., 
''iO' J ^fi'''^^ <ir untl a11 v °n need. Box 
<» &%v& 8ize WxlO'xS- (parts 

Sgc3) <? [g?' avail. aep.I. Send only 

39/6 + 4 <J V. & P. Money 
back guarantee. 

CONCORD ELECTRONICS LTD. (P.E.11) 

8 Westbourne Grove, London, W.2 
(nr. Bayswater Tube) (Callers 9-6 inc. Sat.) 




AUDIO EFFECTS 

5 SHAW LANE, HALIFAX, YORKS. 

Buy with confidence and obtain the right results. 
Refunds without question If any of our products 
fail to give 100% satisfaction. 

AMATEUR BANDS ALL TRANSISTOR 
SCPERHET RECEIVER KIT. So fuss, I* drilling. 
Just fit the components on our printed circuit. Slow 
Motion toning. Simple IK alignment. Perspex front 
panel. Push pull AF amp drives jour 8-15 ohm 
speaker. Amp can be used ut paratflv. Designed tu 
accept a BFO signal, t'scs Deuco plug in colls 
2T. 0-5 to 1-54 Mhz 3T. 107 to 5 3 Mhz 

4T. 5-0 to 15 Mb* ST. 10 5 tu 31 a Mhi 

Range 3T normally supplied with kit. Cses 9 Volt 
battery. Easy step by step instructions. Complete 
Kit. aj.19.6 plus Sj'il P.P. ,v Ins. Extm ranges 
12/- per range. 

POWER CONTROLLER. Power at your finger 
tips. Mot merely halt wave control but full wave, 
A single variable control gives zero to lull power. 
Uses latest 15 amp 3k\V trlac and special triggering 
device. Ideal for all types ol lighting, fires, motors, 
drills, etc. Complete with bos, power socket, 
cables, etc. In kit form with easv to follow instruc. 
tions te.9.6. Ready built £9.4.8 plus 5,6 P. P. & Ins. 

REVERBERATION AMPLIFIER. Self contained 
transistorised, battery operated. An entirely 
different approach to sound reproduction. 
Normally, sound reproduction from a single source, 
has a fiat one dimensional effect. With this unit, 
proper sound delay through reverberation, tones, are 
created with a truly third dimension for concert 
hall originality. Two controls adjust volume and 
reverberation. Simply plug microphone, guitar, 
etc., in, and the output Into your amplifier. Supplied 
In a beautiful walnut cabinet "Jin ■: 3in 4 J in. 
tlO.4,0. P. P. £ Ins. fl.-. 

VOX SWITCH. This sound operated switch is ideal 
tor mobile TX work, tape recorder switching, etc, 
You speak, it snitches. High and medium imp. 
inputs. AF take off point. Drives vour IS volt 
relay. In kit form with full instructions Kit. 
Ready built, tested and guaranteed. 69/8 post paid. 
METRONOME UNIT. Variable beat. Listen while 
you play and keep In time. Easily built, pocket 
size with personal mini earphone. In kit form 27,8, 
post paid. Ready built In an attractive polythene 
case, 37/ 8 post paid. 

MORSE OSCILLATOR. PC board, transistors, high 
stab, components, battery carrier, ear piece. Adjust- 
able tone. Just attach your key. Drives phones or 
speaker. In kit form 17/8 post paid. Beady built 
In similar case as above £7'6 post paid. 

STRAIGHT FROM THE PRESS. Latest Mullard 
manual: Audio Amps. KM tuners, Stereo decoder, 
Receiver circuits, Hi Fl, Tape, etc., etc. 32/ 8 post 
paid. 

TEXAS TRANSISTORS. Complementary symmetry. 
Driver, NPN, PNP output. The set of three 
ONLY 6/6 post paid. 



gline studios limited 

PRINTED CIRCUITS AND PRECISION 
PHOTO MECHANICAL REDUCTIONS 



Coplhorne Road, Felbridge, Surrey 
Telephone: East Grin stead 23540 works 



Your local component stockist 

ast Anglia 

AGLE 

lectronics 

agle St. 




PSWICH 



58075 



Practical Electronics October 1970 



839 



DIOTRAN 



SALES 

P.O. BOX 5 
WARE, HERTS 
TEL: WARE 3442 



SIL. G.P. DIODES 

JOOmW 30 10/- 

40PIV (Min.l 100 30/- 

Sub-Min, 500 £5 

Fully Tested 1,000 19 

Ideal Tor Organ Builders. 



Post and Packing coses are continually r-sing. 
Please add 1/- towards same. CASH WITH 
ORDER PLEASE. GIRO No. 30-101 

OVERSEAS QUOTATIONS BY RETURN 
SHIPMENTS TO ANYWHERE IN THE 
WORLD 



OYER 2 MILLION SILICON 



TRANSISTORS 
Type and Construction 
A 1 Germ. A.F. NPN TO- 1 
A 2 Germ. A.F, PNP TO-5 
A 3 Germ. A.F. PNP T0-I 
A 4 Germ. R.F. PNP T0-I 
A S Germ. R.F. PNP T0-S 
A 6 Germ. V.H.F. PNP TO 



ALLOY », GERM. TRANSISTORS AVAILABLE FOR 
IMMEDIATE DELIVERY 

Qty. 



Price 
100 
= ACI27, NK.T773, ACIS7, ASY86 £3.10 
= ACY 17-21, NKT237-245 CI 

= ACI28, NKT271, 2G3BI CI 

= OC<M-4S. NKT72/I2S, ASY54 CI. 10 
=2N1303, NKTI64-7. 2G30I-3 
= AM 16-7, KNT667, 2G4I7 



C3J0 

A 7 Assorted Germ. A.F. -R.F. PNP mixed cans, general purpose 15s. 

A 8 Germ, A.F. SO-2 PNP =2G37I-B9. ACY27-3I. OC7I-75 £2 

A 9 Sil. Alloy PNP TO-S = 2530 1-5. BCYI7-29. BCY30-34 £2 

AID Si I. Alloy PNP SO-2 =25321-325. OC200-205 £2 

A I to A7 Guaranteed BQ% Good usable Transistors ideal for low cost production work and experimental 

use. A8 to AIO are all perfect devices, factory tested, no open or short circuit Transistors in these lots. 



Qty. 

Price 

500 

£15 

£3 

£3 

£4. 10 

£4,10 

£15 

£2.10 

£7,10 

£7.10 

£7.10 



Qty, 

Price 

1 ,000 

£25 

£5 

£5 

£7.10 

£7.10 

£25 



£12,10 
£12.10 
£12.10 



Qty. 

Price 

10,000 

£200 

£40 

£40 

£60 

£60 

£200 

£32 

£100 

£100 

£100 



BRAND NEW FULLY TESTED EPOXY CASE | 
UNIJUNCTION TRANSISTORS. Type TIS43 and 
BEN 3000 and replacement for 2N2646, Full data available. 
LOWEST PRICE AVAILABLE ANYWHERE. 100 off 4'- 
each =£20; 500 off J 6 each =£87.10; 1 ,000 off 3 - each = 
£150. Sample devices 7,- each on request. 



HIGH QUALITY SILICON PLANAR DIODES. 

SUB-MINIATURE DO-7 Glass Type, suitable replacements 
for OA200, OA202, BAY3B, IS! 30. I $940. 200.000 to clear 
at £4 per 1,000 pieces. GUARANTEED 80% GOOD. 



SILICON PLANAR PLASTIC TRANSISTORS. 

2N3708A VcB30 Hfe 20-60. All marked, rully tested and 
guaranteed. I off 1/6 each ; 100 off lOd. each: 500 off 9d. 
each; I ,000 off 7-Jd. each. 



OA90 GERM. DIODES 30PW 45MA DO-7 GLASS. 

30.000 Available New and Coded. Price £3 per 100. £11 per 
500. £17 per 1,000 pieces. Once sold cannot be repeated. 



FULLY TESTED DEVICES AND QUALITY 
GUARANTEED— SURPLUS TO REQUIREMENTS 
OA202 Silicon Diode, Fully Coded, 
I 50 PIV 250mA Qty. Price £30 per 1 .000 pieces. 

02A00 Silicon Diode. Fully Coded. 
50P1V 250mA. Qty. Price £25 per 1 ,000. 

BYIOO SIL. RECT'S BOO PIV 550mA, 

l-492/6each; 50-99 2/3 each ; 100-9992- each; 1.000 up 

MO each. Fully Coded. 1st Qlty. 



PLASTIC PNP SILICON TRANSIS- 
TORS. Manufacturers' seconds from 
2N3702-3 family. Ideal cheap trans, for 

manufacturing, etc, £8.0.0, — 500. £13.10.0 — 

.000 pieces. 



PLASTIC NPN SILICON TRANSIS- 
TORS, Manufacturers' seconds from 
2N3707-37II family. Ideal cheap trans, for 
manufacturing, etc. £7.10,0—500. £12.0.0 
— I.OOO pieces. 



TO-18 METAL CAN PNP SILICON 
PLANAR TRANS. High quality. 99% 
good. Typesimiliar to 2N2906-7, BC166-7 
8CY70-I-2, £9 per 500. £15 per 1.000 pieces' 



TOP HAT RECTIFIERS. 

short or open circuit dev 
range 25-400PIV. 750mA. 
£12.10.0 per 500. 


Al 

11 


good. 

Vo 

per 


No 
:age 

100, 



S.C.R.'s I6AMP (unplated) 

1-24 25-99 100 up 

I0OPIV, 9;6 7/6 6/- 

400PIV, 14/- 12/- 10/- 

All tested perfect functional devices 
guaranteed. 



16 TESTED TRANSISTORS 



each 

BCI08 
BCI09 
BFY50 
8FY5I 
BFX84 
8FX86 
BFX88 



ONE PRICE ONLY PNP. NPN. 
SILICON PLANAR 1/6 EACH 



1/6 
each 



2N696 
2N697 
2N706 
2N708 
2N929 
2N930 

in: I3i 



2N I I 32 
2NI613 
2NI7I I 
2N2904 
2N2905 
2N2924 
2 N 29 26 



From Manufacturers' Over-runs 



Metal cases. Devices similar to above Nos. 



25733 
2N33SI 
T1S44 
2N2906 
2N2907 
2N2696 
2N3702 
2 N 3703 
-Unmarked Plastic and 



2N2220 

2N3707 

2N37I I 

2SI02 

25103 

2SI04 

2S732 



GERM. PNP AND NPN TRANSISTORS FUT.LY 
TESTED, UNMARKED SIMILAR TO 1/6 EACH 

AC 1 25 ACY22 ACY36 NKT677 OCBI 2G38f 

ACI26 ACY27 NKTI4I NKT7I3 OC82 

AC127 ACY28 NKTI42 NKT773 2G301 

ACI28 ACY29 NKT212 OC44 2G302 

ACI30 ACY30 NKT213 OC45 2G303 

ACY19 ACY3I NKT2I4 OC7I 2G308 

ACY20 ACY34 NKT2IS OC72 2G37I 

ACY21 ACY35 NKT27I OC75 2G374 



2G382 
2G399A 



1/6 
each 



POWER TRANSISTORS 

OC25 OC35 NKT403 ASZI7 

OC26 ADI30 NKT404 TI3027 

OC2B 'AD 1 40 NKT405 

OC29 AD 1 49 NKT452 



5/- 

T 1 3028 narh 
T 1 3029 e * tn 



Manufacturers' Surplus Germ. A.F. All similar to above. 



TRANSISTOR EQVT. BOOK 

2,500 cross references of transistors— British. European, 
American and Japanese. A must for every transistor user. 
Distributed by DIOTRAN SALES. 15'- EACH. 



TEXAS 2G37I A, B 
Eqvt. OC7I Germ, 
Gen, Purpose Trans. 

Each 



1-99 
1 00-499 
500-999 
1000 up 
All Brand 
Coded. 



Vast mixed lot of subminiature 
glass diodes. Comprising of 
Silicon, Germ.. Point Contact 
and Gold Bonded types plus 
some Zeners. 500.000 available 
at Lowest of Low Price. 
1,000 pieces £3.0.0. 5,000 pieces 
£13.10.0. 10,000 pieces £23. 



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1A7CT 7/8 I SoI^KT 8/- ] I>L82 

1H5CT 7 3 ' *2ai:4t;TlLB M/J4 

IN SOT 7 8 SflCl aelDL9li 

JR5 5 8 SeCM 13 - ' DYS« 

I SB 4 3 30C17 IB - DYf 



6/9 I EL500 12/8 PCLS4 7:8 | VBC41 10''8 

S 8 EM34 If 8 I'CLSS 9- 1'BFSft 5 8 

7 3 ' EMSn B'3 PCL86 8/3 

8 3 PCLS* 14 6 



5 S EMS i 
5 9 KM>4 



m 

ss-i 

SV4 



g/B SOCIo 13/6 : BABC80 8 8 BH81 



OYati'l 6/9 

6Z4G 7 f 6 

6/30L2 IB- 

SALS 

BAM''. 

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OATH 

GAUS 

6BAH 

BBEii 

SBJO 

6C5ti 

6F14 

BDF23 

BF-J5 
6J5G 
6KTU 
8K8H 



SO 
78 
73 
B I 



PCLS0015.B 
PE>~-\4 8 8 
PFI.200U 9 
1'LSO 8,9 



LBESU 8 8 
UOC84 7 - 
IX-C85 7. 8 
L'CFSO 7, 3 
1/CH42 12/ 8 
UCH81 8;' 6 
ICL92 7,- 
fCLB3 11;'9 



6 9 30F5 16'- EAF42 10/-- EYol 
fl'.'B 30FL1 12/9 | EB91 2/3 j EY8IJ 

30FL12 14/6 ! EBC3.1 8/- I EZ40 B,'- PL81 9/8 

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30L1 88 EBF.hu 8 8 EZ80 4 8 M3S B8 lF41 10 , £ 

2 3 30LI0 13 - EBra' 8 3 F.ZSI 4 9 PL s4 9 8 

2 9 30L5 7 15 6 ECGS1 3 8 OZ3L! SB PL500 18 <_ 

5/6 30r4 12/- ECCT2 4 8 OZS4 ■ P ,, jM 13 8 

6/- 30P12 13.9 ECC83 7/- i KT41 15, 8 r Tj -, os 33 9 

t/t SOP] 9 IB,'- I ECC8S 5.9 KTIil !9 „.», .. 

*'6 30PL1 12/8 ' ECCH04 IB/- ■ KT6G 188 , £°? piVg 

4.'S 30rLKi 14 8 ECF80 8 6 LX3.TI 14 6 I '^|| ft* 

4 9 3(IPf,H14- ECFS2 6 6 N7S 17; B 



35LfifJT 8/9 ' ECH35 8 '- 
35W4 4/6 EGH42 12,9 



3SZ4GT 6/ 
807 8/- 

m<\.\ 12/6 

AC/VP216/8 

AZ31 

H34i» 



14. J 
1 2 (i 

4 9 

5 8 
29 

63S7f:T 4.3 
6V6G 3/8 
6V6OT 8/8 
fSX4 4,'B 

0X5(iT 68 
10PI8 7,'- . _ 
101?) 3 12- DAF9'i 
12AT" S'fl DF33 
ISUkV* 49 DF91 
12AU7 4/9 DF5H1 
12AXT 4/8 l>H77 
lSKitCT 7/3 I DK3S 
19BC.Iit;17/6 DKB1 
20E2 13'6 j DK92 
20P3 1KB I DK91 
20P4 18/6 ] DE33 



ECH81 Bit 

ECHM 8/3 

ECH84 7,8 

ECL80 7 - 

9/8 1 ECW2 8 B PC9O0 

13 - ECLS'l 8 - PCC84 



P61 10 - 
PABC80 7, - 
PC88 10(8 
I'CSfl 10/3 
PC90 8/6 
PC97 8- 
.6 

b e 



B729 12 6 EF37A 6 8 , PCCS5 8 - 
CCH35 18.6 EEM0 4/8 I PCCS* Br 



PYS'2 
FV33 
PY81 

PY82 

PY83 

PYSS 

PYSOO 

PYS01 

R19 

R20 



10 

IP - 
S 3 
5 3 
5.0 
80 
78 
7 8 
86 

12 



LTSa 
I' FSB 
UL41 
UL44 

VLSI 

u.Msn 

UM84 
1Y4I 
LYS6 



6 8 
8 9 

12- 
BO,- 
fh 
S- 
4/9 

7 8 
5 B 



CL33 18/6 EF41 

CY31 6'9 EFKO 

J)AC;lL] 7,3 EF?3 

DAF91 43 EFSi; 

3 EKSSi 

;B EF!»I 



11/9 I PCC39 8,6 . ,.,. 
4'8 PCC189 9,'fl l2u 
8/3 I PCCS0i51S, , - 2*» 
6 3 t'CFSO 8 6 ' 4 ' 
5 3 PCFS2 8 6 i- 1 
2 9 PCF80 9 6 L 



SU-2150A 
12/ 



2/9 EF1 S3 5 9 PCF800 138 }' '.\* 



7/3 EF184 
4/6 , EH0O 

7,6 EL33 

59 F.I.34 

8 6 EL41 

73 ELS+ 

5- E190 



PCF30I 6 9 l 1*3 
PCF802 B/- I J-.23J 
PCFSOa 13/6 T ; 30 ' 
P€F30U11,8 , L .^ 
PCFSOS14 8 CP* ] 



13, 
18,'- 
13/6 
12.- 

4.'9 
126 

86 
14/6 
10/6 
14/6 
19 8 



VP4B 16/6 
3/6 
W- 

41 
38 

2 6 
7 8 
3.- 

3 - 
■I ■ 
36 
3 I 
5 - 
2 6 

a e 

2 B 

2 8 

;> 
2/« 
0C81D 2/8 
OCS-2 8/8 
0C82D 2/8 



W77 

W119 

Z77 

AC107 

AC 127 

AD140 

AillB 

AF11G 

AF117 

AE125 

AF127 

OC20 

OC44 

OC45 

0C71 

OC72 

OC75 

OC81 



4 B PCT-S2 7 3 IABC80 8 8 ~ 

5 3 PCL473 12 - l'AF42 10.3 0C170 4'8 

READERS RADIO (P.E.) 

85 TORQUAY GARDENS, REDBRIDGE. ILFORD, 
ESSEX. Tel. 01-550 7441 

Pdataee on 1 vnlvc BJ. est! a. Wu 2 »aivea or more, postage Bd. per 
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BAKER 12in. MAJOR £9 

The remarkable quality and performance 
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Major Module 30-17,000 cps with 
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840 



Practical Electronics October 1970 



VALUABLE NEW HANDBOOK 

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Have you had your copy of "Engineering Opportunities"? 



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HENELEC 5-5 STEREO AMPLIFIER, Input* for ceramic cartridge. AUX/Tuner 
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PARTS TOTAL COST 
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AFI05 50kV multimeter (lllus.). 

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£15, p.p. 7/6. 
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33> 



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Everything for the constructor 

Complete with 10/- value discount voucher for use 
with purchase. Price 7/6, p.p. 2/- 

WHY NOT SEND AWAY TODAY? 

New 8-page Semiconductor List free No. 36 new ranges and a fev 




YOU CAN SAVE 25",, brand new GARRARD 

(Post 7/6} COMPLETE LIST FREE ON REQUEST AND GOLDRING 

SP25 Mk.M £10.19.6, AP7S £16.19.6, SL65B £14.19.6. SL72B £25, GL69 £22 

SPECIAL Above with Sonotone 9TAHC diam. Addl 
OFFER £2, with magnetic add 70/-. with Goldring 

G800 add £7.10.0 
Also Fitted with 9TAHC diamond 2025TC £9.15.0. 
3000LM £9.15.0, MODEL 50 £9.15.0 
Plinths/Covers: Standard 99/6, p.p. 4/6. De luxe 
£8.10.0, p.p. 6/-, SL72B type £8,10.0. p.p. 6/-, GL69 
Type £9.15.0, p.p. 6/6. 

9 Goldring GL69 with plinth and cover and GSOO 
cartridge (usually £51) £39.10.0. p.p. 12/6. 




MCIAI 25wa,t an < 



SILICON AMPLIFIERS 




LOOK AT THE 
SPECIFICATIONS ! 

• 0-3% Distortion at full power 
% — Idb I Ic/s to 40kc/s at full power 

• Response — Idb II c/s to lOOkc/s 
PA2S 10 Silicon Transistors, Differential input, 25watt rms into Bohms, 
700mV input. Size only 5' x 3* x 2'. 4-hole fixing. I2wate into ISohms. 
Supplied with edge connector and harness. 

PA50 12-Transistor Version, SOwatt rms into 3 to 4ohms 
MU442 Power supply for one or two PA25 or one PA50 

• PA25 £7.10.0 • PA50 £9.10.0 • MU442 £6 



NEW 



SELF-POWERED 
PREAMPLIFIERS 




Mains operated Slim Design Preamplifiers for use with any ^power »nM>'ifie£ 
AH Silicon FET/TRANSISTOR design. Capable of dr.vmg up to 4-fAW 
amolifiers. Pushbutton selection. All facilities. 

MODEL FETI54 STEREO AMPLIFIf-ft , 

m outs for mag Pick-up. Tuner/Aux.. Tape m and out. Response 20 c/s to 
30keK. Output ad.usuble up to I volt. iJWBI boost or cut-out controls. 
Slim design. Size 12" x S£' x I*', Pnce £16.10.0 



MODEL FET »/L 

Mono Preamplifier with built-in mic. MC X EC input for all crystal and 
ceramic cartridge.. Tuner, tape in and out. D/P and Response as FET 1 54. 
Size I0±' X 4F x If Price £12,10.0. 
NO SOLDERING JUST PLUG IN CONNECTORS 1 



ELECTRONIC ORGANS 



COMPLETE RANGE OF 
COMPONENTS IN STOCK FOR ALL 
PURPOSES 

• MODERN ALL BRITISH TRANSIS- 
TORISED DESIGNS AVAILABLE AS 
KITS OR READY BUILT. VENEERED 
CABINETS FOR ALL MODELS 

• 49 NOTE, 61 NOTE SINGLE 
MANUAL DESIGNS ALSO TWO 
MANUAL 49 NOTE 
1 KITS AVAILABLE IN SECTIONS AS 
REQUIRED 



N EW PA and DISCOTHEQUE CENTRE *t 'MB 




SSBBTfro FOUR ELECTRONICS CENTRES WS 

303 309 354-356 EDGWARE ROAD LONDON W.2